Milling of cases. Milling technology
This raised a lot of questions and discussions in the comments, so we decided to continue this topic and focus on creating prototypes of housings and mechanisms for electronics, so that it would be easier for you to navigate the various materials and prototyping technologies that modern manufacturers offer.
As always, we will pay attention to the most pressing issues and give useful tips, based on our practice:
- What materials are the prototype housings made from? electronic devices?
- Review modern technologies prototyping: what to choose? Here we will look at different 3D printers and compare them with CNC milling technology.
- How to choose a prototype manufacturer, what documents to provide to the contractor?
1. What is the prototype housing for electronic devices made of?
The optimal materials for the electronics housing are selected taking into account the design requirements, the purpose of the device (operating conditions), customer preferences and the price category of the development. Modern technologies allow the use of the following materials for the manufacture of prototypes:- Various types of plastic: ABS, PC, PA, PP, etc. For housings requiring increased impact resistance or resistance to aggressive environments, polyamides and polyformaldehydes (PA, POM) are used
- Metals: aluminum, various grades of stainless steel, aluminum-magnesium alloys, etc.
- Glass
- Rubber
- Wood (various species) and other exotic materials
When combined in one housing various types materials, it is important to get advice from specialists; they will help you correctly implement the joining points, provide the necessary parameters of tightness, strength, flexibility, i.e. will compare the wishes of the client and the device designer with real production capabilities.
2. Review of modern prototyping technologies: what to choose?
Case prototypes can be created on production equipment, but different technologies are used. For example, plastic is not molded, but milled or grown, since creating an injection mold is a time-consuming and expensive process.The most common prototyping technologies today are milling and growing (SLA, FDM, SLS).
Growing prototypes in 3D printers is especially popular; this fashionable technology is rapidly developing and is even layered on mass production. Today, a wide variety of products are grown, including metal products and food products, but all this has its limitations. Let's look at these technologies in more detail, and at the end we'll try to choose best option to create a housing prototype:
SLA (Stereo Lithography Apparatus)- stereolithography technology allows you to “grow” a model in a liquid photopolymer, which hardens under the influence of an ultraviolet laser. Advantages: high accuracy and the ability to create large-sized models. The high-quality surface of SLA prototypes is easy to finalize (it can be sanded and painted). An important drawback of the technology is the fragility of the model; SLA prototypes are not suitable for screwing in self-tapping screws or testing cases with latches.
SLS (Selective Laser Sintering)- selective laser sintering technology allows you to create a prototype through layer-by-layer melting of the powder. Advantages: high accuracy and strength, ability to obtain samples from plastic and metals. SLS prototypes allow assembly testing of enclosures using hinges, latches and complex assemblies. Disadvantage: more complex surface treatment. 
FDM (Fused Deposition Modeling)- technology of layer-by-layer growing with polymer thread. Advantages: the resulting sample is as close as possible to the factory version of the device (up to 80% strength compared to plastic injection). The FDM prototype can be tested for functionality, assembly and climate control. Parts of such a case can be glued and ultrasonic welded; ABS+PC materials (ABS plastic + polycarbonate) can be used. Disadvantages: average surface quality, difficulties in final processing. 
As you can see, the restrictions various technologies cultivations do not allow us to accurately reproduce and convey the tactile characteristics of the body. Based on the prototype, it will not be possible to draw conclusions about the real appearance of the device without additional processing. Typically, growing can only use a limited number of materials, most often one to three types of plastic. The main advantage of these methods is their relative cheapness, but it is important to take into account that the additional processing that is required for high-quality appearance products, covers this advantage. Moreover, the quality of the prototype is also affected by the growing accuracy, which is not sufficient to create small-sized cases. And after processing and polishing the surface becomes even lower.
Wherein milling on numerically controlled machines(CNC) allows you to achieve manufacturing accuracy of one order of magnitude with the accuracy of mass production. In this case, you can use the absolute majority of materials that are used in the mass production of cases. The main disadvantage of milling is its high labor intensity and the need to use expensive equipment, which leads to the high cost of this technology. Although these costs are quite comparable to growing the body, if you take into account the lengthy and expensive final surface treatment.
3. How to choose a prototype manufacturer, what documents to provide to the contractor?
When choosing a contractor for the production of prototypes, you should pay attention to the following features:- Finished prototypes must be fully functional, as close as possible to serial products, so that they can be used for certification, demonstration to investors, at exhibitions and presentations.
- The manufacturer must work with a wide range various materials and technologies, provide advice on their choice. This way you can choose the best option for your specific project.
- It is advisable that the contractor has a database of trusted manufacturers both in the CIS and in Southeast Asia, so that you can receive an assessment of various options regarding the timing and cost of manufacturing the various components of your device. This will make it easier to choose the best option.
We hope our tips will help you create your own
Housings for electronic devices/microwaves, heat sinks/radiators for electronics, as a rule, contain small structural elements: threads for fastening printed circuit boards, holes for connectors, grooves for laying and fixing sealing gaskets, etc. Universal machining centers are often not able to quickly cope with milling small elements of electronic devices due to the low rotation speed of the cutting tool, so high-speed 3D CNC milling is optimal.
High-speed 3D CNC milling of aluminum is a modern, dynamically developing area of metal cutting. With this type of processing, classical formulas for calculating cutting forces do not work, because the speed of intermolecular rupture of metal differs significantly from the speed of metal separation during standard “power” milling.
During high-speed milling of aluminum, the importance of removing heat and chips from the cutting zone increases, so cooling is carried out using technical alcohol supplied to the cutting zone using compressed air. This provides additional advantages in the absence of the need to wash parts after milling - aluminum and copper housings for electronic devices / microwaves, heat sinks / radiators for electronics, come out literally shiny.
Also, one of the undeniable advantages of high-speed milling is the cleanliness of the processed surfaces. High-speed 3D CNC milling allows, without grinding, to obtain the required parameters of roughness and flatness of heat-removing surfaces of REA / microwave housings and heat sinks / radiators of radio-electronic devices.
High-speed milling requires the purchase of special, expensive carbide tools. Unfortunately, “standard” cutters are not suitable for this type of processing, and this significantly narrows the choice of cutting tools.
Another advantage over “standard” milling is that “drilling” holes for various diameters of blind or through threads can be done with one carbide milling cutter at high speed without the need to change the cutting tool. This significantly reduces processing time and, as a result, becomes cheaper.
Mechanical threading in instrument housings for electronic devices/microwaves often leads to breakage of the taps inside the almost finished part. This increases the cost of parts for the Buyer, because The supplier has to include additional costs for technological stock into the cost of manufacturing the batch. Also, a negative factor in metalworking threading in aluminum, copper and plastic is the low quality of the resulting threads: lack of perpendicularity to the main surface, “jamming” of the first turns of the threads being cut due to the need to repeatedly screw in and turn out the taps.
High-speed 3D CNC milling of aluminum allows you to avoid this problem: thread milling is carried out with special carbide cutters moving along a spiral path.
Another serious problem in the manufacture of “species” housings of REA / microwave units is manual machining of chamfers, burrs and sharp edges, because It is very difficult to achieve high quality of processed surfaces of aluminum parts manually.
High-speed 3D CNC milling of aluminum, copper and plastic allows you to remove chamfers, burrs and sharp edges with high speed, accuracy and quality using special carbide countersinks. This type of milling processing significantly increases the consumer qualities of manufactured products and reduces the risk of specific parts becoming defective.
