In the past fifteen years, major progress has been made in prototype replication. Initially, most RP technologies have obvious advantages in terms of speed, but due to issues such as accuracy and material properties, they limit the further development of the technology. Since the advent of the RP, due to the threat of certain competition, the CNC has also brought about well-known benefits when its speed has been improved. The same RP has also been improved in accuracy, material properties and surface finish.
Understanding these two techniques is particularly important for choosing the right tool for the job. The following guidelines can help with the choice of tools.
Materials
RP is restricted
The study of materials has gone through a long process. The range of material choices has increased and performance has been guaranteed. Currently available materials are metals, plastics, ceramics, and composites. The choice of materials is still limited. Moreover, the performance of most materials does not match the performance of the material in terms of processing, molding and casting.
CNC machining is virtually unlimited
Machining centers can do cutting processing on almost all materials.
The maximum size of the part
The maximum size of RP is 600x900x500mm
Although existing industrial equipment cannot process dashboards or baffles, existing prototypes can be used to produce most of the daily and industrial products. If the part to be produced by the equipment is too large, its various components can be produced first and then finally joined into a complete part. It must be noted that size has an effect on time and it takes longer to make larger parts.
CNC machining can produce aircraft parts
The size of the actual parts and modules that CNC machining can produce is as small as a desktop device to a bridge device. It can be said that the limitation of the CNC size only comes from the mechanical tools used.
Complexity of parts
Unlimited RP
If a sample can be molded with design software, the time or cost of manufacturing is virtually unaffected. Rapid and cheap production of complex parts is one of RP's greatest strengths.
CNC machining is limited
CNC machining must deal with all the details of the components. As the complexity of parts increases, the number of required equipment and changes in tools will increase accordingly. Large aspect ratios, deep grooves, deep holes, and square corners all increase the cost of CNC cutting equipment. Five-axis cutting tools and certain techniques can overcome these deficiencies, but simple operations such as undercutting can also cause problems.
Details
RP has its own unique place
The RP can process some details that the CNC can't do. For example, the RP can machine sharp internal angles, can process deep and narrow channels, high and thin walls, and prisms that are characteristic of large aspect ratios.
CNC has its own difference
The CNC has many features that can outperform the RP, such as sharp edges, smooth overlays, and clean chamfers. This is especially important when assessing details about accuracy, ie surface finish.
Accuracy
The accuracy of RP is 0.125～0.75mm
The accuracy of some individual sizes of RP may exceed 0.125mm, but its general deviation range is 0.125-0.75mm. Accuracy varies with the RP device and size. The size increases and the accuracy increases.
The precision of CNC is 0.0125-0.125mm
If the machining equipment is appropriate, the accuracy may be very high. Under normal circumstances, the accuracy of the CNC is higher than that of the RP, and the accuracy is generally related to the cost of the equipment.
Repeatability
Low repeatability of the RP
RP is sensitive to many factors that affect the quality of prototypes. Parts may be manufactured at different times and the results may be different. Temperature, humidity, positioning, and placement are just a few of the parameters that can affect product repeatability.
High accuracy of CNC machining
The CNC machining repeatability is much higher than that of the RP. If the tool path, tools and materials used are not changed, the repeatability of the product will be higher. Environmental conditions and human factors can affect the results. For some materials, temperature and humidity can affect production because they can affect the accuracy of the equipment used by the technician.
Finishing
Ra value of RP is 2.5 to 15 microns
If you do not do the secondary treatment, if not all, there are some rough surfaces. RP uses certain techniques to increase the thickness of the sheet to 0.0125 to 0.025 mm, but the lamination and irregularities of the sheet still affect the finishing of the sheet. If you want to do the secondary treatment, you can achieve the desired level of finish, but doing so will change the accuracy of the part size. At the same time, these operations also add extra time and cost.
CNC processing Ra value 0.5 to 5 microns
Machining, unlike RP, can make prototypes, models, and tools suitable for the surface finish they require. For RP, secondary treatment (sanding, polishing) can improve the surface finish, but it also affects the accuracy, time, and cost.
Reliability
The reliability of RP is medium
For most technologies, product reliability increases as the product continues to mature. RP technology has only 15 years of history, which means that it has different levels of reliability. Due to the short time and resource scarcity of this technology, some RP manufacturers do not have much time to improve the device components in order to improve their reliability.
Reliability of CNC machining is medium to high
CNC has been researching and developing for more than 30 years, so it is a trustworthy and reliable technology. Over the years, continuous technological improvements have eliminated equipment components that produce reduced product reliability.
Required operator
RP requires very few operators
With the exception of secondary operations (such as placement of racks), the RP requires very few people. Within minutes, it can prepare the necessary information for the parts and start manufacturing. During manufacturing, little or no human involvement is required.
CNC machining requires many operators
Although CAM software applications have been improved, in most cases they still cannot eradicate human intervention. Installation and operation of the equipment requires experienced technicians; it is extremely rare that the model is manufactured in unmanned conditions.
Required experienced mechanic
Craftsmanship required by the RP is minimal
The wages of the employees of this technology are certainly not the lowest, but the number of experienced skilled workers is less than that of machining. This statement is somewhat true because the technology itself does not require any workers. In addition, the RP is improved and the operation process does not even require skills.
The number of skilled workers required by CNC
Machining requires skills, creativity and problem solving. From toolpath design, machining strategies to cutting operations and monitoring, machining is done by experienced technicians. As the company's revenue decreases and the number of technicians declines, it is likely that the company will lack the human resources needed to make models.
Development cycle
RP requires short to medium cycles
RP is less sensitive to the complexity of the design because it requires fewer employees, fewer operating steps, it not only reduces the actual manufacturing cycle, but also reduces the overall process time. Overall, RP technology is efficient in both time and manpower. If the RP receives data at 4:30 PM, the product can be produced the next morning. For CNC, if there is no production time for two classes, absolutely no product can be produced. However, this is not to say that RP technology is the fastest for any part.
The period required for CNC machining is medium
There are many things involved in machining, mainly manpower, tool trajectories, fixtures, processing time and materials. The result is that a lot of work takes much more time than RP. However, if the design is simple and easy to understand, the CNC can also shorten the cycle; if the shaft speed is fast, the feed rate can also be changed.