Since its invention in the last century, CNC has been widely used around the world and has become an indispensable part of many industries. As the world’s leading on-demand manufacturing provider, Elimold has noticed that most customers are trying to reduce CNC machining costs. We believe that there is no fixed cost that can be universally applied to different machining projects, and it is usually determined by several factors. So, how can we better control the cost of CNC machining? Let’s take a look at the information we have summarized over the years of experience.
CNC machining fee calculation formula
CNC machining price calculation: CNC lathe processing fee: The standard calculation method is working hours * wage per working hour + fixed expenses that should be allocated, such as depreciation. The processing fee of a general CNC machining center is 40-50 US dollars per hour. The machine tool is about 1 meter long, and it is an ordinary vertical machine tool. The price is slightly higher by more than 10 US dollars in places with fewer machine tools. Of course, the price will vary depending on the processing capacity of the machine. Therefore, we can see that the main factor affecting the cost of CNC machining is processing time. Therefore, when designing parts, we should pay attention to avoid designs that increase processing time.
Factors Affecting the Price of CNC Machined Parts
The cost of CNC machining is usually determined by multiple factors (material cost, machine time, labor cost, design and programming cost, etc.). Based on the above information, you can calculate the final cost of CNC machining. And be aware that the cost of CNC machining will be affected by many other factors (size and shape of the part, condition of the machine and tooling, batch production, etc.). Therefore, we should avoid the following factors when designing machined parts.
Minimum R angle
CNC milling cutters have a cylindrical shape. When cutting the inner wall, a radius will appear on the vertical angle. Small tools can be made multiple times at a lower speed to obtain a small radius, which will result in more time and higher costs. Therefore, when you design a part made by CNC machining, it is best to increase the cavity depth radius and use a similar radius for the inner edge. If you do not provide a 2D drawing to specifically indicate that the right angle needs to be cleared, all the right angles of the inner cavity of the workpiece can be processed with the minimum R according to Elimold’s rules;
If the workpiece needs to retain the right angle, please provide a 2D drawing annotation, and the spark machine discharge clearing is required (clearing the angle requires CNC machining the copper male and then discharge machining on the spark machine, which is more expensive), or change the workpiece structure, make the R angle avoid the empty space, and CNC directly process it, which is less expensive. If the workpiece has through holes on both sides, it can be cut and processed on the wire cutting machine to clear the angle, which is more expensive.
Thread design
In order to reduce communication costs and avoid processing errors, it is recommended to design the thread according to the standard drilling inner diameter and rolling outer diameter, and to fully describe the thread parameters. When placing an order, try to put the matching internal and external thread workpieces on the same order for processing; each engineer draws a different 3D drawing of the thread bottom hole diameter. If there is a special thread, it is best to provide a real object for adaptation; and sometimes the design may not require a long thread length at all, but the design drawing has a long threaded hole, which may require special tools during the processing process, and requires more processing time and cost. Therefore, we recommend that the thread length should not exceed 3 times the hole diameter. When the threaded hole is a blind hole, it is recommended to leave a thread-free length of at least half the hole diameter at the bottom of the hole.
Cavity Depth
Machining deep cavities greatly affects the cost of CNC parts because a large amount of material needs to be removed, which is extremely time-consuming. CNC tools have a limited cutting length and work best when they are cut 2-3 times their diameter. For example, a ø12 milling cutter can safely cut cavities up to 25mm deep. Cutting deeper cavities (5 times the tool diameter or more) can lead to problems such as tool overhang, tool deflection, chip evacuation difficulties, and tool breakage, so special tools or multi-axis CNC systems are required. In addition, when cutting cavities, the tool must be tilted to the correct cutting depth, and smooth entry requires sufficient space. Limiting the depth of all cavities to 5 times their length (i.e., the maximum dimension in the XY plane) minimizes machining costs.
Notes on thin wall thickness
Thin wall machining requires multiple passes at low cutting depths, which is prone to vibrations that can cause deformation or breakage. Therefore, thin walls are difficult to machine accurately and the machining time will increase. The wall thickness of metal parts should preferably be designed to be above 0.8mm (minimum 0.5mm), and the minimum wall thickness of plastic parts should be above 1.5mm (minimum 1mm).
Tolerance considerations
The tighter the tolerance, the higher the processing cost because it increases the processing and quality inspection time. If there is no specific tolerance marked on the part drawing, it will be processed according to the standard tolerance (±0.1mm or higher). If there is a special tolerance processing requirement, be sure to provide a 2D drawing and mark it accordingly.
Notes on 2D drawings
2D drawings are the best way to convey certain aspects of a design. Clearly marking tolerances, surface roughness, assembly methods, key inspections, and quality control for key features will provide a reference for selecting the best processing method and process route, and will also reduce costs;
Threaded holes and dimension depths also need to be marked simultaneously; engineering reviewers will also compare 3D and 2D drawings, and if there are conflicts, they can communicate and feedback in a timely manner.
Production Volume
As the number of parts increases, the unit cost of a group of identical parts decreases significantly. This proportional reduction in cost is primarily the result of eliminating duplicate design costs and machine setup commissioning. CAD design, CAM preparation, and machine setup are all done once for all parts to be manufactured. (That is, if you produce one part, the design cost and machine setup cost are included in this one part. If you produce 1,000 pieces, then the design cost and machine setup cost are evenly distributed over these 1,000 pieces)
Structural Design
The more complex the part structure, the higher the manufacturing cost. Highly complex parts may require more advanced machinery. They also require more processing time, multiple assembly and disassembly and equipment setup, more resources and closer inspection. All of these will affect the cost of the part. In CNC machining, certain part features and designs will inevitably increase costs.
Thin-walled design
Parts with thin walls will take more time to process because they are very fragile. And because they often vibrate or deform, it is difficult to maintain accurate tolerances, and in more serious cases, they may break. Slow processing, special processing techniques and high scrap rates make these thin-walled parts more expensive. Thick-walled parts are more stable and cost less to process. To keep the processing price low, please avoid thin-walled design. The wall thickness of metal parts should be greater than 0.8mm and the wall thickness of plastic parts should be greater than 1.5mm.
Designing features that cannot be CNC machined
Not all features can be CNC machined. A typical example is a 90° internal angle, because all current CNC milling tools have a cylindrical shape, which will produce a fillet instead of a right angle or other sharp angle when cutting the edge of the cavity. If a right angle must be left, the usual way to achieve this goal is through EDM (Electrical Discharge Machining), which is a more expensive manufacturing process than CNC machining. If the fillet cannot be left for assembly reasons, it is recommended to use the internal fillet method.
Designing for larger internal corner radii
Although the corner radius can be reduced by using a smaller diameter tool, this means that multiple passes are required at a lower speed. This is because a smaller tool cannot remove material in a single pass as quickly as a larger tool. Therefore, small fillets will also increase machining time and cost. It is recommended that the fillet radius R is at least 1/3 times the cavity depth D.
Surface structure features
When designing CNC machined parts, simple structures should be the principle, and complex surface features should be reduced. In order to obtain complex surfaces with suitable surface finish, small cutters are required. These small cuts take much longer than normal cuts, which increases costs. Therefore, in order to help minimize costs and processing time, minimize or avoid the use of surfaces. For example, when chamfering the outer edges, if it is not necessary, chamfer instead of rounding.
Designing holes of standard sizes
Using standard drill bits allows for fast, high-precision CNC processing of holes. From an economic point of view, it is best to use standard hole diameters. For non-standard hole sizes, end mills must be used, which may increase costs. In addition, generally speaking, the larger the hole, the deeper it can be drilled. It is recommended that the drilling depth should not exceed 10 times the diameter of the drill bit.
Avoid unnecessary text and lettering
Adding text features to the surface of CNC machined parts should be avoided, as designing text through CNC machining will only increase machining time and cost.
Material cost
The material cost involved in manufacturing parts is one of the most important components of part cost. The material cost is composed of the cost of raw materials, the amount of materials used, and the processing time of materials.
Design suggestions to reduce the cost of CNC machined parts
Based on our years of experience, Elimold has summarized some suggestions that can effectively reduce the cost of CNC machined parts.
Choose cost-effective materials
Soft materials are preferred. For parts that do not require high strength, soft materials such as aluminum alloy and brass can be selected. These materials are not only easy to process, but also reduce tool wear and processing time, thereby saving costs. In addition, waste can be reused. In CNC processing, waste treatment is an important link. By reasonably designing and optimizing cutting paths, reducing waste generation, or reusing waste, material costs can be effectively reduced. According to our experience, using suitable materials can save about 15% to 20% of production costs.
Optimize design and reduce complexity
Try to avoid unnecessary complex structures and use standardized designs as much as possible. When parts require curved surfaces and grooves, try to use fewer curved surfaces and grooves to reduce the difficulty of processing, shorten processing time and reduce the number of tool changes. Therefore, if the design requires the use of multiple tools, each tool change will increase the time cost. Therefore, consider using a simple design to reduce the processing tool sequence and processing time. By optimizing the design, not only can the difficulty of CNC processing be reduced, but also the delivery cycle can be shortened. In Elimold’s experience, design optimization may save up to 30% of costs.
Mass production improves production efficiency
By standardizing the production process, the additional costs brought by personalized customization can be reduced. In addition, in mass production, machine tools can continuously process the same parts, reducing the time and error of each setup. In addition, for mass-produced parts, the use of multi-axis CNC machine tools for processing can greatly improve production efficiency and reduce overall costs. According to Elimold’s internal data, mass production can reduce the processing cost of each part by about 40%. Therefore, for companies that need to mass-produce parts, mass processing can not only improve efficiency, but also significantly save expenses.
Summary
CNC machining cost control is a systematic project, which involves the purchase and maintenance of equipment, scientific selection of materials, training and management of personnel, and fine control of the production process. Only by considering all aspects comprehensively can the overall cost reduction be achieved and the quality of the product be guaranteed. However, reducing the cost of part manufacturing is essential for companies to maintain competitiveness, profitability and adaptability in dynamic market conditions. But remember that cost reduction should be balanced with other factors such as quality, delivery time and reliability. Communicate openly with your CNC machining service provider, provide clear specifications, and work together to find cost-saving opportunities while maintaining the quality and functionality required of the parts.