Twenty20 Version 2

Twenty20 Engineering 3D Printing Capabilities

TDG91 — Wed, 20 May 2020 09:39:24 +0000

Introduction

As said many times Twenty20 Engineering is proud to say it has its own in house 3d printer. We use in the prototyping stages of design development for checking form fit and function of components or assemblies. This helps ensure both we and our clients are 100% happy with design before proceeding to manufacture. This enables us to avoid costly re-work and delays when providing our services to our customers. Another added benefit is that we can help our trusted network of manufacturers be confident that what has been designed is possible to manufacture and assemble.

Twenty20 Engineering has a small FDM machine and has a trusted manufacturer with a larger machine and SLS capability. We see Additive Manufacturing an area where further development will happen quickly, not just in polymers but metals. In future we will be looking to invest further in the technology and are looking for opportunities to develop metal 3D printing, particularly WAAM Weld Arc Additive Manufacturing technology.

Twenty20 Engineering 3D Printer

Twenty20 Engineering has a desktop 3D printer – Tier Time UP Mini 2 ES. This is a small 3D printer but has similar features to the much larger industrial 3D printers. This small machine packs a punch, with single head extrusion, heated chamber, and air filtration system. It can accurately and reliably print most filament materials.

Tier Time Up Mini 2 ES Specifications

Printing Technology	FDM (Fused Deposition Modelling)
Extruder	Single
Nozzle Diameter	0.4mm
Extruder Maximum Temperature	299℃
Extruder Maximum Travel Speed	200 mm/sec
XYZ Accuracy	5, 5, 5 micron
Connectivity	USB Cable, Wi-Fi, LAN, and USB Stick
Display	4.3″ Full Coloured LCD Touchscreen
Build Volume	120 × 120 × 120 mm (4.7″ x 4.7″ x 4.7″)
Printed Object Accuracy	±0.1mm/100mm
Layer Resolution	0.15/0.2/0.25/0.3/0.35 mm
Build Plate maximum Temperature	70℃
Calibration and levelling	Automatic Nozzle Detect
Build Plate Surface	Perf or Flex, Heated
Pause to Change Filament Type	Yes
Filament Materials	ABS, ABS+, PLA, TPU
Filament Diameter	1.75mm

The below video shows the unboxing, setup, and calibration process for setting up the machine for the first time.

There are some limitations with the machine, bed size and single head extrusion being the main 2. Due to this Twenty20 Engineering has access to the below machines through a trusted manufacturer.

Trusted Manufacturer Machines

Our trusted manufacturer has an industrial sized FDM machine and an SLS 3D printing capability. They are a specialist in 3D printing and has several years’ experience within the field and offer a wealth of advice and support.

Stratasys F170 Specifications

This is an accurate industrial sized, double extrusion head machine developed by the company behind FDM technology.

Printing Technology	FDM (Fused Deposition Modelling)
Extruder	Double (Dissolvable Support and Material)
Nozzle Diameter	0.1mm
XYZ Accuracy	2, 2, 2 microns
Connectivity	USB Cable, Wi-Fi, LAN, and USB Stick
Display	6″ Full Coloured LCD Touchscreen
Build Volume	254 x 254 x 254 mm (10in x 10 in x 10in)
Printed Object Accuracy	±0.1mm/100mm
Layer Resolution	0.330, 0.254, 0.178, 0.127 Material Dependant
Build Plate maximum Temperature	90℃
Calibration and levelling	Automatic Nozzle Detect
Build Plate Surface	Removable base plate, on steel bed
Pause to Change Filament Type	Yes
Filament Materials	ABS, ABS+, PLA, ASA
Filament Diameter	1.75mm

EOS P100 Specifications

This is an accurate industrial sized, accurate and versatile SLS machine. This machine is leader of the pack when it comes to this technology.

Printing Technology	SLS
Laser	C0₂ 30W
Precision Optics	F-theta lens
XYZ Accuracy	2, 2, 2 microns
Connectivity	USB Cable, Wi-Fi, LAN, and USB Stick
Build Volume	200 x 250 x 330 mm (7.9in x 9.8 in x 13in)
Printed Object Accuracy	±0.1mm/100mm
Layer Resolution	0.1mm

3D Printing Materials

TDG91 — Thu, 07 May 2020 13:20:52 +0000

Introduction

When it comes to what materials can be used in 3D printing the sky is almost the limit, the large number of different manufacturing processes ensure there is a wide variety of materials that can be used. The list of materials available is growing, as demand for different mechanical properties increases due to the proliferation of 3D printed components and assemblies.

The types of materials available can be easily categorised in to 3 distinct groups, liquid resin, filament, and powder. The 3 manufacturing techniques covered in our An Introduction to 3D Printing use these 3 categories, SLA uses liquid resin, FDM uses filaments and SLS uses powder.

How the component is expected to perform once manufactured will directly impact the choice of material and the manufacturing process. For example, if the component needs a high strength to weight ratio FDM and an ABS filament should be used. Whereas SLA resins should be used for rapid prototyping full colour concept models and architectural models, and SLS using a nylon-based powder can be used to rapidly test injection moulded components.

Producing metal components for example in the aviation sector is possible using SLM (Selective Laser Melting) which is remarkably similar in principle to SLS. However, the powders used are metallic and completely melted rather than sintered.

There is a downloadable material mechanical properties datasheet attached to the bottom of this article and on our downloads page.

SLA

There are several different materials that can be used with the SLA manufacturing process. All begin life as a liquid and then are selectively cured by a UV laser to create the component.

As with all photopolymers the printed parts do not last indefinitely as they deteriorate over time due the UV in sunlight, becoming brittle and breaking apart. Therefore, SLA is used for rapid prototyping and not manufacturing end use components.

There are several resin manufacturers such as Somos and Formlabs who produce photocurable resins. listed below are 5 materials and a brief description which can be used to demonstrate different properties:

Poly1500
- Translucent appearance
- Properties comparable to Polypropylene (PP)
- Impact resistant and durable
- For large rigid functional prototypes

Credit: https://www.materialise.com/en/manufacturing/materials/poly1500

ProtoGen – White
- White or coloured appearance if dye is added, or component is painted
- General purpose material with similar properties to ABS
- Useful for concept models with high levels of detail that need to be durable, e.g. impellers

Credit: https://www.forecast3d.com/materials/sla

Tusk C2 700T
- Translucent material with blue tint
- Strong water-resistant
- Similar properties to ABS and PBT
- Ideal for high end models for the architectural/ construction sector or water flow analysis

Credit: https://www.materialise.com/en/manufacturing/materials/tuskxc2700t

FDM

FDM is a very versatile method of 3D printing, because the material that can be used have a wide range of mechanical properties. The quality of the filaments is comparable to injection moulded components. This enables the production of low-cost final use components for large assemblies at a reduced cost, as there is no need for expensive tooling.

The ability to swap between materials easily on the same machine makes this method suitable for batch manufacture. The material is stored on a spool and is fed through a heated extrusion head. In to change materials it is a simple case of swapping spools and purging the extrusion head of the previous material.

Again, there are several different manufacturers of filament material, however because of the significantly lower cost of the machinery it is mush easier to source. With individuals and companies able to approach suppliers. There are many different type and grades of firmament available, so the list of 4 below concentrates on the main types:

ABS
- Printed ABS is 80% strength of injection moulded ABS
- High strength to weight ratio
- Good quality surface finish with post processing
- Many different colours
- Water resistant
- Ideal for snap fits, end use components, jigs, and fixtures
- Suitable for concept modelling, testing for form fit and function

Credit: https://www.3dhubs.com/knowledge-base/post-processing-fdm-printed-parts/

TPU
- Flexible and touch thermoplastic
- Impact resistant
- Non-food safe
- Hydroscopic and ill absorb moisture from the atmosphere
- Ideal for concept testing of flexible, rubber like components such as custom phone cases, O-rings, RC car tyres etc.

Credit: https://www.simplify3d.com/support/materials-guide/flexible/

PLA
- Biodegradable, renewable source plastic (it is made from sources such as corn starch)
- Stiff and lightweight but can be brittle
- Low glass transition temperature and melting point.
- Exceptionally good interlayer bonding and produces fine detail.
- Suitable for prototypes to check fit, form and function
- Not suitable for end use components like ABS

Credit: https://www.simplify3d.com/support/materials-guide/pla/

Polycarbonate (PC)
- Widely used thermoplastic
- Excellent impact resistance
- Temperature resistant both high and low
- Flexible with a high tensile strength
- Suitable for end use components

Credit: https://www.simplify3d.com/support/materials-guide/polycarbonate/

SLS

SLS printing uses a laser to trace out 2D slices of a model over a powder bed. The laser fuses the powder particles together it does not completely melt them. Using the SLS printing method allows for complex geometries to be constructed as the un-sintered powder is used as a support material for the component.

Although fast production of components is possible, consideration must be given to the properties of the component. The components will have a powdery look and feel even after post processing such as dying and polishing. The models will also be porous and if using Polyamide (Nylon) powders, they will also be water absorbent and subject to swelling and distortion.

SLS is a useful process due to large build platforms and the ability to nest parts in the bed for batch production. Although large thin, flat surfaces and small holes tend to warp and distort. There are a wide variety of materials that can be used with this technique.

PA12
- Excellent general-purpose material
- High elongation before breaking
- Medium strength
- High flexibility
- Low water absorption
- Recyclable material

Credit: https://www.prodways.com/en/material/pa12-l-1600/

Polypropylene (PP)
- Extremely easy material to print with
- Suitable for applications with snap-fits, ductility and living hinges
- 10% light than PA12
- High chemical resistance
- Suitable for small and large components

Credit: https://3dprintingindustry.com/news/prodways-unveils-new-promaker-p1000-x-sls-3d-printer-and-materials-156008/

TPU
- Tough and flexible material
- Durable
- Elastic with 300% elongation at breaking point
- No infiltration
- High resolution

Credit: https://www.prodways.com/en/material/tpu-70-a/

An Introduction to 3D Printing

TDG91 — Tue, 28 Apr 2020 15:58:31 +0000

Introduction

3D printing is a relative newcomer to the manufacturing sector as it has only been around since 1983, 37 years at the time of writing this. Compared with other forms of more traditional manufacturing that have been around for thousands of years. Although the machine and control systems are much more complicated now, the basic principles of turning, milling, cutting and drilling for example remain the same.

There are 3 categories which all methods of manufacturing can be divided into. 3D printing or to give its technical name Additive Manufacturing is the newbie of these and has its own category.

The 3 categories are:

Subtractive
- This is where material is in the form of a billet or sheet. Unwanted material is subtracted from the original material until the desired component is achieved.
- Methods of subtractive manufacturing include cutting, drilling, turning and milling
Formative
- Where a material is processed into the desired shape, and there has been no loss or gain of material to create the component. Material may require a change in state.
- Methods of formative manufacturing include drawing, forging, rolling, bending, injection moulding and casting
Additive
- This is the process of joining materials to make components from 3D model data, usually layer upon layer. The opposite to subtractive or formative manufacturing.
- Types of Additive Manufacturing include:
  1. Stereolithography (SLA)
  2. Digital Light Processing (DLP)
  3. Fused Deposition Modelling (FDM)
  4. Selective Laser Sintering (SLS)
  5. Selective Laser Melting (SLM)
  6. Electron Beam Melting (EBM)
  7. Laminate Object Manufacturing (LOM)
  8. Binder Jetting (BJ)
  9. Material Jetting (MJ).

Broadly speaking all types of Additive Manufacturing follow the same production process. However, the method of manufacturing the 3D printing machines uses is different. This article will focus on the more popular manufacturing processes, Stereolithography (SLA), Fused Deposition Modelling (FDM) and Selective Laser Sintering (SLS). Further information regarding the other manufacturing techniques can be found here https://3dinsider.com/3d-printer-types/

There are so many different types of Additive Manufacturing, as each is suited for different materials and components, each have advantages and disadvantages. For example, it is extremely hard to use FDM to manufacture a translucent component, but it is possible (and more expensive) to do so using SLA and the correct polymer resin. It also worth bearing in mind that like 2D printing and traditional manufacturing each type has differences in

Cost
Quality
Speed
Capability
Practicality
User Expectation
Material and mechanical properties

Production Process

The flow diagram below shows the main stages of the production process for all types of 3D printing

SLA

SLA is a rapid prototyping process, which has a seriously high level of precision and accuracy. It can produce dimensionally accurate components within a few hours of the model data being uploaded to it. The process is popular for components requiring fine details and exactness.

SLA printers do this by converting liquid photopolymers, (a specialist plastic) into a solid component using an ultraviolet laser. The resin is heated in a bath to start the state transition to a solid, and the laser using mirrors to direct the beam in the X&Y axis to trace a 2D slice of the component over the surface of the resin to complete the transition to a solid. The bed of the machine moves downward, the top of slice is covered with resin using a recoating blade and the laser traces again. The cycle continues until the printer has completed all the slices. This builds the component from the bottom up. (some printer now do this vertically to remove the need for a recoating paddle or blade).

After the printer has finished operating some post processing is required to complete production. The part is removed from the resin bath and any support structure is cut away. The component is post cured in an ultraviolet oven, to ensure the resin is fully cured. Depending on the quality required the component maybe hand sanded and polished, paint can also be applied if required.

Credit: https://openi.nlm.nih.gov/detailedresult?img=PMC4345107_jds-16-1-g001&req=4

The top 5 advantages and disadvantages of this process are:

Advantages

High precision, fine detail and accurate parts can be produced
Translucent or clear components can be manufactured
Extremely large components can be manufactured up to 2m in size.
Resin material not solidified can be reused
Production of flexible and rigid components.

Disadvantages

Only photo sensitive polymers can be used
Machinery is relatively expensive
Material will degrade over time, from the UV in sunlight
Components will be fragile compared to other additive manufacturing techniques
Higher levels of health & safety required, the resins are not the most pleasant substances and the laser is relatively powerful

This short video from Protolabs best explains SLA printing,

FDM

FDM is what 90% of people think of when they think of 3D printing. This process was developed by Scott Crump and implemented by Stratasys Ltd, a major player in Additive Manufacturing. This method uses production grade thermoplastics such as ABS, TPU, Nylon and PLA to name a few, to print components. This method of Additive Manufacturing can produce functional prototypes, concept models and final assembly components. It has a high level of accuracy and precision, as well as producing components with a high strength to weight ratio.

To start this process, as always, a 3D CAD model needs to be generated and sliced into 2D layers. The printer then builds the components by heating a thermoplastic filament, and extruding this through a nozzle, once the 2D slice has been printed the bed moves down. The next layer is the applied to the previous layer and the process continues. Additional material is kept on a spool within the machine.

Some machines have more than one extrusion head to allow multiple materials to be extruded for example an ABS head and dissolvable support material head for more complex geometries. As well as this manufacturing spec 3D printers used in factories have enclosed heated chambers and to slow the rate of cooling of the extruded thermoplastic, this increases the mechanical properties of the material and prevents warping and bending due to thermal shock.

Like most Additive Manufacturing techniques there is a level of post processing after the components have been printed. They will need submerging in a heated bath with a bleach solution to remove any support material. The components can also be sanded and polished to blend the ridges created by each layer of printing.

Credit: https://www.dddrop.com/fdm-technology/

The top 5 advantages and disadvantages of this process are:

Advantages

Material flexibility, enables the easy change of material for different components and mechanical properties required
High strength to weight ratio of the printed components
Wide variety of machines available from the hundreds to tens of thousands of GBP
Dissolvable support material enables easy creation of complex geometries
Easily accessible to non-experts within industry

Disadvantages

Component accuracy and precision can suffer from poor quality slicing.
Nozzle size limits the level of fine detail achievable
Deformation and delamination of components due to fluctuations in temperature during build
The reliability of machinery can be poor, especially using cheaper machines
“Stringing” where excess material is not properly layered from the extrusion nozzle

Stratasys has this great video demonstrating FDM 3D printing,

SLS

SLS was developed by an American businessman and inventor called Dr. Carl Deckard, who patented the technology in the mid-1980’s. The technique utilises high power CO2 lasers to fuse particles together (SLS is very similar to SLM, but doesn’t melt the powdered material).The laser sinters powdered material together in layers, materials that can be used include white nylon, ceramics, powdered metals and even glass.

The process works by a laser tracing out the 2D slice of the component in X&Y axis over the powdered material. The build platform then moves incrementally down, and a roller or paddle moves across the surface of the powder and finished layer of the component, burying the component in a fine layer of powder. The laser passes over again to complete another 2D slice until the full component has been manufactured. Large complex geometries can be manufactured because the un-sintered powder is used as support material for the rest of the component.

Once the printer has finished the component post processing can commence. This usually involves shaking or using and airline in a controlled, ventilated environment to remove excess un-sintered powder which can be reused. The component can go through a finishing processes such as sanding, polishing and dying to improve the finish quality of the component.

This technology produces fully functional prototypes and end use components, which are durable, high precision and accurate. SLS is remarkably like SLA, regarding speed, accuracy and quality although the materials and their mechanical properties are vastly different.

Credit: https://www.livescience.com/38862-selective-laser-sintering.html

The top advantages and disadvantages of this SLS Printing are:

Advantages

Large complex geometries can be produced
No extra support material required, and un-sintered material can be reused
Highly accurate and precise so can produce fine detail
Can be used for prototyping and functional end use components
Parts easily nested within the bed for rapid batch/medium volume production

Disadvantages

Industrial machinery is only available currently, and is expensive
Components appear to have a grainy surface finish even after post processing
Components tend to have high porosity so will absorb moisture unless treated during post processing
Large flat surfaces and small holes are extremely difficult to print accurately as they are susceptible to warping and over sintering
Special health and safety measures need to be utilised when working with lasers and finely powdered material.

Solid Concepts has a great video demonstrating SLS production process,

COVID-19 Face Mask Ear Guards

TDG91 — Wed, 22 Apr 2020 13:38:29 +0000

3D Print File for NHS Heros

At Twenty20 Engineering we have seen some images of health
care workers who’ s ears have been rubbed raw due to face mask elastic around
their ears. We have also seen some great examples by individuals donating ear
guards made on 3D printers at home or even knitted.

So, we thought we could help. A design has been created and the .STL file has been made downloadable from our website, which is ready to print. We encourage those who have a 3D printer or know of any companies or schools that have access to one to download this, create the ear guards and donate them to health care workers and local hospitals (contact your local hospital for more details on how to do this safely).

Twenty20 will be printing several of these and donating as
well.

A few details:

Print time approximately 20 mins
Recommended material is PLA or TPU
Can be stacked when using dissolvable support material
Recommend a solid fill, not honeycomb.

3D Print File for NHS Heros

Time Lapse – Mechanical Analysis FEA Video

TDG91 — Mon, 20 Apr 2020 13:02:59 +0000

This is a short FEA time lapse video demonstrating the mechanical analysis of a small Stainless Steel 304 link component. Larger ring is fixed, with the smaller ring having 300N load applied putting the link component under tension.

Things to bear in mind, regarding the results of this video:

Deformed result shown during the Von Mises stress plot has been exaggerated 2300 times
Minimum Factor of Safety was 12.1
Displacement results not shown.
Link component performed as expected

This video has been created for demonstration purposes only.

The Impact of using FEA during the Mechanical Design Process – 5 min read

TDG91 — Thu, 09 Apr 2020 12:14:53 +0000

Introduction

There has been an increasing use of FEA over the last two decades in a wide variety of industries and applications, as access to stand alone software and 3D Cad software add-ins has increased. The increasing user-friendly interfaces of standalone software such as Ansys and Abaqus FEA and the inclusion of software add-ins to 3D CAD modelling packages such as Simulation in SolidWorks has helped drive this. It is becoming increasingly common that FEA is included as a standard part of the Mechanical Design Process.

What is FEA?

FEA, or Finite Element Analysis is the simulation of any given physical phenomenon using a numerical process called Finite Element Method (FEM). Engineers use this process to reduce the number of physical prototypes, testing required or optimise the design of a component or system. FEA is carried out during the design phase to rapidly develop better products in a reduced time frame.

The types of simulation that can be carried out are as varied, as the industries they are used in, below is not a definitive list but gives an insight in to what is possible:

Linear Static Analysis
Dynamic Analysis
Frequency & Buckling
Non-linear Analysis
Thermal Analysis
Fatigue Analysis
Computational Fluid Dynamics (CFD)

FEA however is not a silver bullet to all of challenges that engineers face. These methodologies although computerised are based on partial differential equations that have been developed by very astute mathematicians, scientists and engineers. They have been created from copious amounts of experimental data to provide an accurate set of equations, which describe the physical phenomena encountered within engineering.

These equations do not provide definitive and finite answers though and are solved iteratively to increase accuracy. Due to this no FEA model will ever be 100% accurate, it can only provide a very close approximation to the actual outcome. As with all engineering products prototypes and physical testing should always be used in conjunction with FEA, to prove the concept of the design.

It would appear then, that there is a contradiction in the name of the process and mathematics behind the software. It is called Finite Element Analysis, because the user must put a limit to the number of calculations carried out by the software i.e FEM. This depends on several factors:

Accuracy
Computing power required and available
Time
Experience of the engineer

What is the process?

FEA within the design process follows a similar journey from project to project, it may be repeated several times depending on the outcome the results. This may be to further optimise the design or because the design has not performed to the desired criteria. This increases the speed with which informed design decisions can be made before prototyping, testing or manufacture.

Applications of FEA

There are many industries that make use of different types of FEA, some are more obvious than others. FEA is best used when complex relationships and geometry are to be studied that would be hard to calculate manually, for example the dynamic loading of a suspension arm on a mountain bike.

FEA while useful, should not be used where the benefits are minimal or can be achieved using simpler means, due to the added steps within the design phase. An example of FEA overkill would be to calculate the stress and deflection of a cantilever I-beam where hand calculations, industry standards and legislation already provide the guidelines for the safe design of such systems.

Another way of thinking about whether FEA is required would be safety, for example during the design and testing of a new pressure vessel. It would be necessary to ensure the safety of the design before undertaking the testing of a prototype, due to the inherent risk of failure.

Examples of where FEA is used are easy to find, but here are just a few:

Linear Static Analysis –
- Structural loading of a complex mounting bracket
Dynamic Analysis –
- Dynamic Loading of a mountain bike suspension arm
Frequency & Buckling –
- Loading of structural beams and columns in a suspension bridge
Non-linear Analysis –
- Compression of a rubber mounting bush for a marine diesel engine
Thermal Analysis –
- Analysis of heat dissipation from a computer heat sink
Fatigue Analysis
- Number of cycles a shock absorber can last before failure
Computational Fluid Dynamics (CFD)
- Aerodynamic improvements to a 44-tonne truck to improve fuel efficiency.

Advantages and Disadvantages

There are several advantages and disadvantages that FEA can bring to a design project. For each project, the team or design engineer must weigh these up during the initial phases of their design framework. To decide, whether FEA is the right tool to use, and how it is implemented will seriously impact the desired outcome of project.

Advantages

Can provide accurate data on complex interactions and geometries
Increase safety of components and systems for prototyping and testing
Reduce project development times
Reduce cost of testing regimes, as unworkable solutions are eradicated sooner
Increase creativity of the design team, by providing results quickly from virtual testing

Disadvantages

FEA is never 100% accurate, due to underlying mathematics and simulation assumptions such as using completely homogenous materials, with no imperfections or impurities
FEA should be used in partnership with testing of prototypes, to prove a design works satisfactorily. It is not a substitute for testing.
The results provided are only as accurate as the parameters defined within the simulation. i.e a poor simulation = inaccurate/misleading results. (Garbage in = Garage out)
FEA simulation packages and software add-ins can be an expensive investment for companies to undertake, especially if multiple licenses are required
Computing power required is very high, meaning additional investment in the right computers may be required
An experienced Engineer will be needed to interpret the results from a simulation, and how best to make changes to the design which will improve specific performance criteria.

Conclusion

It can be seen by how FEA has been used and developed that is a very powerful tool in a design engineers’ workshop. It has helped create components and systems that have never existed before, and more than likely would not exist with without its use. It is only from the results generated from these simulations more efficient designs have been created, increasingly quickly. Using FEA aids creativity and helps to prove and improve a concept before prototyping and testing to back up in the real world what has been predicted virtually.

There are however disadvantages and drawbacks to using FEA which can hamper the development of new designs. Yes, it can point the way to new and novel concepts, but these must be approached with caution. If the simulation is misleading, inaccurate or incorrectly interpreted then any advantages are lost to the designer.

When thinking about whether FEA is worthwhile for an engineering project it is best ask these 3 questions:

What am I trying to learn from the simulation?
How will the results be interpreted and implemented?
Is the success of the engineering project dependent on FEA analysis being carried out?