Rapid Prototyping of Metal Components - CNC Machining
19 Jan 10
Plenty has been written and spoken about techniques for rapid prototyping plastic parts and most designers are familiar with 3D printing methods such as stereolithography, laser sintering, fused deposition modelling and objet or polyjet printing. But what if your prototype needs to be made from metal? What are your options for manufacturing a few parts cost effectively?
The discussion following will seek to answer this question and show you how to get low-volume metal components manufactured at low cost. The simplest way to do this will be to explain the techniques available and suggest some typical applications. Part one of this discussion will look at CNC machining and the following articles will discuss other techniques.
CNC Machining
CNC machining is often thought of as a medium to high volume manufacturing method. However, CNC machining is also a cost effective method of producing complex shapes with little restriction on the materials being used.
For almost any metal part prototyping operation using CNC machining, the key advantages of the process are the wide range of materials available and sheer speed at producing parts. The main drawback can be the programming and setup time but this can easily be off-set by producing more than one component.
For most basic, prismatic shapes the CNC programming can be carried out very quickly on the machine console resulting in low setup costs and fast machining times. But when the shapes are complex is where CNC machining really comes into its own as a rapid prototyping technique.
5 axis, 6axis and multi-tasking CNC machines in the hands of an operator who knows how to use them can produce amazingly complex parts in a single setup with high accuracy. Never assume your component needs to be machined in costly multiple setups until you have consulted your machinist. We have seen many examples of components that we thought were not possible to do in one setup but have been machined perfectly. This is typically achieved using high speed machining techniques which reduces the cutting forces enabling the machinists to use only a thin piece of the parent material to hold the job in place.
Click here to find CNC machinists with 5 axis or 6 axis capability.
The following are some examples of applications for CNC machining as a prototyping technique.
Consider a designer who is developing a complex aluminium casting. The component is ultimately to be high pressure diecast which can mean in excess of $1 million for the aluminium moulding tool. But the designer needs to test the design prior to going into full production and also needs the prototype to look like a casting for a presentation he needs to give the boss. In this example, the casting design will likely have draft everywhere on the 3D model to enable the diecasting to be pulled from the molding tool.
The complex casting can simply be machined using 3D contouring techniques which will machine the entire component including all of the draft angles from the exact intended material. This component can be fully tested for form, function and fit and any adjustments made to the design. This eliminates potentially costly tool modifications when the diecasting mould is made and a prototype can be produced in only a few hours.
For the presentation, the component simply needs to be sandblasted. Sandblasting an aluminium component that has been machined with all of the draft angles on it results in a part that has an appearance almost identical to a cast part. The sandblasting will also nicely remove any burrs and smooth over any machining marks.
In another example, a prototype titanium medical implant needs to be produced. The shape is complex and it must be made from implantable grades of material. In this example, an investment casting could be used but the completed casting will still need to be machined, finished and polished after casting. Thus the casting option will require multiple setups for the different processes to be used and the material may not be readily available due to requiring a furnace change-over. Casting for medical implants also needs to be carried out carefully so as not to introduce any contaminants into the body that may have been trapped in the molten titanium.
Or CNC machining can be used to produce the prototype implant in a short period of time. Firstly, the material will be readily available in bar form complete with material certification. A CNC machinist with good experience in titanium machining will be able to produce the component with extreme accuracy and excellent surface finish requiring very little finishing operations. CNC machining is also a readily accepted manufacturing method for producing titanium implants.
Click here to locate machinists of titanium implants.
Another example is the case of a designer requiring a metal component that has been hardened but has very close tolerances. In production the component may be cast, forged or machined then heat treated and finished by grinding. but in this case to produce the component quickly, the material can be pre-hardened and machined while in its hardened condition using high speed machining techniques or ceramic tooling. The advantages in this case is there is no need to try and predict how the material will distort during heat treatment, for small components the heat treatment can be done in-house using simple equipment and the entire component can be manufactured in one machine as the grinding can be eliminated.
Click here to locate machinists with high speed machining expertise.
This example also applies to other hard materials where the final production of hardened steel, tungsten or ceramic components may be done with MIM, sintering or CIM carrying a high tooling cost. A CNC machinist with the right tooling and CNC machine can machine hard materials as they are. hard material machining for prototype metal components can easily save a great deal of cost and time before moving to full production tooling.
These are only a few examples of applications for CNC machining for the production of prototype parts. There are many more simpler examples and often the basic shape and quantity make CNC machining the obvious choice. But in most cases where the prototype component needs to be produced fast, CNC machining is the first port of call.
In our next edition of this series of articles, we will discuss production of sheetmetal components. The following list are the topics to be covered in the series (these will be linked as the articles are published):
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