1. Introduction to CNC machining
Machining operations seem easy, simple and possible now because of Computer numerical control (CNC) machining, a subtractive manufacturing process that removes layers of material from a job piece in order to produce a customized part using materials like metals, plastics, wood, glass, foam, and composites. It can also be used in telecommunications business and aircraft parts, which have higher tolerances, compared other industries.
Figure 1: CNC machining
1.1 Importance of CNC Machining in Custom Parts Production
CNC machines are extremely advantageous, which is why CNC parts have grown in popularity in the automotive, aerospace, medical, manufacturing, and defense sectors.
- Optimal Productivity
CNC machines are computerized which is why they don’t rely upon manpower once the setup is done. Therefore, CNC machining offers increased productivity than other machines.
- Agile Technology
CNC machines allow the production of sophisticated custom parts at reasonable cost. At low cost, this machining also allows for the design change as per the customer’s needs.
- Fast production
CNC machines are computerized using special software, which obviously results in fast fabrication of customized parts. With CNC machining, not only manual labor is reduced but consistency of parts for low-medium volume production is also ensured.
CNC machines have lower labor costs, boosted productivity, and timely meeting of delivery rates due to its faster production rates.
- Ideal for prototyping
Rapid prototyping is one of the features of CNC that makes it different from other methods of production. With rapid prototyping, the designs can be tested on a small scale and defects can be corrected. This allows the production owners to overcome long term while enabling them to reach smaller customers.
- Compatible with a diverse array of materials
CNC is flexible in terms of materials; it can work with almost all sorts of materials like metals, plastics, ABS, ceramics, foam, wood, composites etc.
- Maximizes efficiency and accuracy
CNC machining results in faster production, high level of production and since it is customized it also results in accurate productions (free of human error). These all characteristics results in maximized efficiency.
- Safer production
Manpower is only required for initiating the machine for the setup. Manpower is not exposed to the machine during the fabrication process which makes CNC machine an epitome of safer production.
1.2 Understanding CNC Machining
For video (reference): https://www.youtube.com/embed/v4jwVdFsoGo
The step by step process of CNC machining is:
- Create a CAD model displaying tolerance, construction lines, threads, etc.
- Then the CAD model is to be converted into a CNC-compatible format, which can be done using CAM tools like AutoCAD, Fusion 360, etc.
- In the final step, machining process will be started by the operator when he/she attaches the required cutting tools.
Microprocessor is the main constituent of CNC machines that is attached to the tool in order to control it. The G-code and M-code programming language are used in CNC to feed the information about feed rate, spindle speed, cutting tool, and coolant flow to the microcomputer. All data processing is done in the MCU, (MCU creates motion commands and delivers them to the drive system). The feedback signals received in MCU are compared to the standard signals where if any faults are detected, new signals are transmitted to the machine tool to carry out the required actions.
There are a variety of CNC machines like CNC milling machines, CNC lathes, CNC routers, CNC plasma cutters, CNC electric discharge machines, and CNC laser cutters.
1.3 Key considerations in CNC Machining
a. Material Selection for CNC Machining
The selection of materials impacts the whole process of machining; its entire lifecycle including prototyping, production, defects, repairs etc. Identifying the material requirements, exploring potential materials, and then choosing the most suitable material are key considerations in ensuring best product outcomes.
The selection of the right material for CNC machining projects involves considering several important factors such as:
Different application require different kinds of material properties. Some application may require high ductility, whereas some may require brittleness, some may require high strength, and some may require greater toughness and so on. Aluminum is used in the aerospace industrial as it has high strength-to-weight ratio.
- Operating conditions
Materials may react differently in different operation conditions such as temperature variations, exposure to chemicals, UV radiation, water contact, and flame resistance. Proper understanding of the effect of environment conditions with the materials is required.
- Dimension / Tolerance
Industries like aerospace require dimensionally stable components with precise tolerances. The materials those are malleable, ductile, properties that make them machine-able are preferred in these industries.
- Electrical Conductivity
Some applications may require the material to have high conductivity while some process may require them to have insulating properties. For excellent conductivity, materials like copper, silver can be used and for insulating properties, PTFE (polytetrafluoroethylene) may be chosen.
- Physical Appearance
Some customers may prioritize the aesthetics of the finished production as their major requirement. Depending on your customer’s desire, maintaining the physical appearance and focusing on secondary finishing operations may also be essential.
Whatever a customer is paying for the product, it should be worthwhile of their time and money. Materials with better properties and failure resistance are expensive. Careful evaluation of the toughness, strength, hardness, wear resistance, corrosion resistance etc. is necessary to determine if a material can serve as a cost-effective alternative.
Proper research regarding the availability of the materials is to be done before finalizing the material. A material can have everything your process requires, but if it is not available abundantly, that material has to be replaced with one that is available to you locally or in some easy, indirect ways.
b. Design Considerations for CNC Machining
- Inner Edges
While dealing with inner edges, a vertical corner radius should be of at least 1/3rd of the cavity depth. Slightly larger corner radius results in higher surface finish quality.
- Thin Walls
If the wall thickness is decreased, it causes the decrement of stiffness of material. This in turn causes vibrations to increase which results in higher errors. Recommended wall thickness values are
According to design recommendations, flat-bottom holes should be avoided as much as possible. To make deeper holes, specialized drill bits (minimum diameter of 3 mm) are employed.
4. Smaller Features
Similar to the flat-bottom holes, micro-machining (process of creating cavities and holes having diameter of less than 2.5 mm) is recommended to be avoided unless absolutely required.
5. Chamfers & Fillets
Chamfer edges are recommended to be at a standard 45° angle unless some other angles are absolutely necessary. For fillets, the radius of interior fillets is recommended to be higher than 1/3rd of the depth of the cavity for preventing tool breakage.
1.4 Choosing a CNC Machining Service for Custom Parts
Before choosing a particular CNC machining service, it is vital to consider several factors such as:
- Cost and turnaround time
A customer has a set budget and timetable for their projects. The CNC service they select should be able to work with this cost and timeframe.
- Manufacturing Capability
Before choosing a vendor for CNC machining process, reviews of other customers, their history etc. should be assessed by the customers. Vendors should be prepared to demonstrate why they are the better choice and why they should be chosen over other potential vendors.
Ask these questions to all the potential vendors before selection of one.
- What is the average turnaround time for a CNC project like mine?
- Do you have prior experience in cutting the materials that my project requires? Can you provide me the information regarding the type of tools and materials that you usually work with?
- What are the limits of the size of an object that can be cut?
- What kind of axis does your CNC machine possess (5th, 6th, or 7th)?
- Do you outsource your work? If yes, what platform do you use?
- Are there any other services that you provide?
1.5 Future trends
- Use of Plywood in Laser Cutting
Creation of geometric patterns and etch designs on wood is possible nowadays, all thanks to CNC laser cutting techniques that helps in maintaining the strength, flexibility and durability of milled wood.
BoXYZ machine is the one that combines two technologies of 3D printing and CNC machining. It is an all-in-one device that integrates a CNC mill, a laser engraver, and a 3D printer. Because of its versatility in work, it is tremendously growing in popularity.
3. Machining Ice
Japan has started using CNC machines in order to create intricate sculptures out of ice. By converting vector information into G-code and M-code, CNC machines care now able to mill ice into detailed and beautiful shapes.
4. Machine Alerts on Smartphone
It is not necessary to watch the machining process to receive updates on where the process is at. A system has been developed in your smart phones that can send alerts through texts, emails. It is capable of sending the users real-time information about the condition and status of their machines.
CNC machining services have revolutionized the production of custom parts by offering unparalleled precision, speed, and versatility. This advanced technology empowers businesses and individuals to bring intricate designs to life with exceptional accuracy and efficiency. With the capability to work with a wide range of materials and provide extensive customization, CNC machining fosters innovation and facilitates the creation of high-quality, distinctive parts.