What is CNC Prototype Machining and How Does it Work?

What is CNC Prototype Machining and How Does it Work?

Computer Numerical Control, or CNC in brief, has revolutionized how manufacturing is done. Technology has been around for over 70 years, becoming the main pillar for modern-day production and finding applications in each and every manufacturing sector.

CNC prototype machining is one such area in which the technology has proven to be a boon. Prototype machining is an indispensable process for every industry. Therefore, manufacturers often wonder about the best method to create prototypes of machined parts.

This article will explore what prototype machining is and how CNC has impacted this segment. It will also cover the pros and cons of CNC prototype machining, and mention several tips to optimize the processes to create prototypes.

What is Prototype Machining?

Prototype machining, also sometimes referred to as prototyping machining, prototyping process, or simply prototyping, is the process where a manufacturer creates a small batch of the final part, with intention of a production run later.

The purpose of the prototyping stage is to convey visual information about the final parts, find out how a digital design turns out physically, and determine the product’s properties.

Functional prototypes of final parts also enable the manufacturer to identify any defects in the design and eliminate them before manufacturing large quantities of the product. The elimination of defects in the prototyping stage makes the overall production run cost-effective.

Is CNC Machining Good For Prototyping Processes?

Although many now consider 3D printing to be the dominant form of rapid prototyping, CNC machining is also an important process for creating prototype parts. To say that Computer Numerical Control (CNC) machining is good for the prototyping stage would be an understatement. In reality, CNC is the go-to technology whenever prototype machining processes are required.

CNC technology uses computerized controls for monitoring the movement of the cutting head and workpiece. The movement can be done in the slightest intervals that are not even possible if you choose alternative prototyping processes.

CNC prototype machining starts by creating a 3D CAM model of the final product. Once the model is completed, it is converted into a CAD design. Unlike the Computer-Aided Manufacturing (CAM) file, Computer-Aided Design (CAD) file is understood directly by the CNC machines since this file contains instructions for the machine on how to operate.

CAD designs are converted to CAM files, which contain the G Code and M code. G code signifies movement and M code relates to the general operation of a CNC machine, like coolant control.

Example of CNC machine prototyping for a metal part

What are the Advantages of CNC Prototype Machining?

When wondering whether to choose alternative prototyping processes or CNC machining centers for prototypes, these advantages of CNC machining are important to consider:

From file to prototype

One of the biggest advantages of CNC machining is the “CNC” element. Since CNC machining is a digital process that creates a part from a computer file, engineers know that a machined prototype will closely match the digital 3D design, and that the same digital design can later be used to create a final part with identical dimensions. The degree of repeatability is particularly high.

Furthermore, using digital 3D designs allows for quick and precise alterations. If a machined prototype exhibits a physical flaw resulting from bad design, the engineer can return to the CAD software to make suitable changes for the next prototype. Different versions can be compared side by side, and simulation software can even be used to preemptively test how a part will perform in the real world.

Repeatability and Consistency

Unlike alternative prototype processes, a CNC prototype has a high degree of repeatability. This means that any finished product manufactured by CNC machining will be the exact replica of any other finished product that uses the same process and design.

Repeatability is very important for the purpose of prototype machining centers. Prototypes are supposed to be identical copies of the design. This precise imitation is only possible with low tolerances that CNC offers.

High Precision

Due to the high control over the movement of the cutting tools, CNC machining has a high precision, low tolerances, and high accuracy. This precision is essential in prototypes to make them accurate to the original purpose. Additionally, since the machining process is accurate, manufacturers know that the flaws in the manufactured prototype are present in the design.

Time-Saving Process

CNC prototype machining does not require any mold or time-consuming prerequisites. Therefore, it is a high-speed process. The ability to modify design files also gives the machining centers the option to make changes to the prototype, take it through CNC machining again, and have it back in no time.

Cost Effective

With CNC prototype machining, the manufacturer ends up saving money in the long run. This is because since the defects and errors can be rectified in the small prototype batch, instead of carrying out the defect in the large quantities of final part in the production stage.

Additionally, any future changes require small modifications to the CAD designs instead of creating a new design from scratch.

Material Versatility

Unlike other manufacturing processes like 3D printing, CNC prototype machining has a wide range of material options. These material options range from the strongest metals and alloys to materials like wood and plastics. Therefore, the prototyping process can be done on the same material as the final component, which is a great advantage for the purpose.

For instance, there are not many methods fully capable of sheet metal forming. This makes the CNC machining service ideal for metal prototypes that have higher mechanical stability and don’t exhibit weakness.

Some of the common material options that work well with CNC prototype machining services are:

  • Aluminum
  • Steel
  • Stainless Steel
  • ABS
  • Magnesium
  • Titanium
  • Zinc
  • Brass
  • Bronze
  • Copper
  • Teflon
  • Polycarbonates (PC)
  • Polypropylene (PP)
  • Polymethyl Methacrylate (PMMA)
  • Polystyrene (PS)
  • Polyoxymethylene (POM)
  • PAGF
  • PCGF
  • Low-Density Polyethylene (LDPE)
  • High-Density Polyethylene (HDPE)

 

3D CAD file Plastic CNC prototype

Limitations of Prototyping Processes With CNC Machined Parts

When it comes to prototyping, using the CNC method is the best way to go ahead. However, some other characteristics of this process can be seen as cons of the process. These cons include:

Subtractive Process

CNC machining is a subtractive process, which means that it creates the final part by removing material from an initial, bigger block. This can lead to increased material usage compared to additive processes that work by adding material into the final part shape. The machining centers incur higher material costs due to increased material usage.

Some Geometrical Restrictions

Since CNC prototype machining works from the outside in, there are certain geometries that cannot be manufactured using this process. This is especially true for the internal components of a prototype. Other processes like additive production work from the inside out, so they can manufacture the internal geometries in a better way.

Technical Expertise

There is a certain technical knowledge required for CNC prototype machining. There is software knowledge required for making CAD designs. Operating the CNC machine itself requires a particular skill set.

Expensive Than 3D Printing

Since manufacturers incur higher material costs, CNC prototype machining is costlier than 3D printing. However, it is important to note that the higher cost comes with added precision and the ability to work on a wider range of materials.

In the case of other processes like 3D production, you are limited to plastics like PLA. While PLA is considerably cheaper than metal blocks, its other characteristics don’t always fit the prototyping requirements.

Prototype done by 5 axis CNC Machining

Applications of CNC Machined Prototypes in Industrial Manufacturing Process

CNC prototype machining is used in the Research and Development process in every sector. Some of the industries that rely on it heavily are:

Automotive Industry

CNC is the go-to process for the designing of parts and models in the automotive industry. The automotive industry requires gears and parts with ultra-high precision. Only CNC machining prototypes is fully capable to fulfill this requirement instead of any other methods.

Aerospace Industry

Aerospace industry constantly goes through CNC machining prototype to test the performance of new innovations in parts and materials. These parts go in aircraft and monitoring equipment, so extreme care is required to ensure that they function to the fullest.

Architecture and Construction Industry

CNC machining is extensively used in architecture and construction for making interior and exterior elements. In the early days, the process was accomplished using injection molds which led to increased time and costs. However, CNC machining prototypes has made it faster and cheaper.

Medical Industry

The medical industry is evolving at a rapid pace, with new medical equipment and prosthetics providing new possibilities for treatments. All these medical equipment require precision on a microscopic scale and hard materials. The CNC machining process provides the highest quality for manufacturing functional prototypes for such equipment since other methods don’t have the required precision.

Military Industry

Military industry consumes a significant portion of the budget of any economy and a major fraction of this budget goes towards R&D. Military R&D involves making new weapons, warfare vehicles, aircraft, and parts for each of these. Since most of it uses metals or even harder materials making rapid prototyping useless, CNC machining prototype is utilized in every step of military R&D.

Oil & Energy Industry

The oil industry requires parts with high physical strength that can mine exceptional depths in the earth’s surface and extract the resources. These parts are crafted using CNC milling prototyping or other CNC machining methods. In energy industries, CNC machining prototypes are used to explore green energy options that reduce environmental impact.

CNC Prototype Machining vs 3D Printing

Professionals often debate about the best prototyping method and the debate is between two technologies- CNC machining and 3D printing. Here is an overview of the differences between the two technologies compared on the basis of the factors that matter:

Working Principle

CNC machining is a subtractive manufacturing method. It takes a big block of material, cuts removes unwanted material with a cutting tool, and shapes the material block into the final part. On the other hand, 3D printing is one of the additive processes. It works by starting out from nothing and adding material a little at a time by melting and forming it into the final part.

Supported Materials

CNC machining supports various materials, from metals to wood and plastics. However, 3D printing is severely limited when it comes to supported materials. It only works in making thermoplastic prototypes because this method works by reheating and shaping the material.

Possible Geometry

3D printed parts can have complex internal geometries because these parts are made from inside going outwards. However, since CNC machining uses a cutting tool on the outside, it cannot make functional prototypes with complex internal geometry.

Wastage

CNC machining, being a subtractive manufacturing method, leads to a lot of material wastage. However, the waste material costs can be recovered by selling recyclable waste material. 3D printing has good material utilization because of additive manufacturing.

Manufacturing Time

While 3D printing is called rapid prototyping, CNC machining is significantly faster. 3D-printed parts take many hours to manufacture a single piece. However, CNC machining can create tens of parts in that same time frame.

Rapid Tooling: Injection Molded Prototypes via CNC Machining

Rapid tooling is a manufacturing technique that allows the production of machined tooling such as dies and molds in a fast timeframe. This machined tooling is manufactured through CNC machining technology. The tooling is then used to create a prototype through injection molds.

Rapid tooling is very different from rapid prototyping, and the two should not be intermixed. Rapid tooling utilizes the advantages of CNC machining service and injection molding while eliminating the disadvantages of each process. By creating machined tooling with CNC and the final part with an additive method like injection molding, manufacturers are able to save costs while retaining some of the precision.

In case CNC prototyping is used to create a prototype, it leads to higher material costs. In case injection molding is used for prototyping, it takes longer and the parts are not imitations of the design. Therefore rapid tools provide a midway between CNC prototyping and rapid manufacturing.

Tips For Preparing Quality CAD Models For Prototype CNC Machining Process

The final part quality of CNC machined prototyping can vary depending on the CAD file used. These designs not only convey visual information, they also provide important dimensions for the components. Therefore, good part quality prototypes require a good-quality CAD model. Here are some tips to achieve that:

Optimizing Design Elements

It is important to optimize design elements such as cavities and holes when using CNC machines. For instance, in the case of end milling, the maximum depth obtained is three times the diameter of the tool. Therefore, specify and limit the dimensions of such cavities.

Ideal Wall Thickness

When creating drawings, be careful of the minimum wall thickness. Too thin walls can lead to the reduced mechanical stability of the CNC custom parts and exhibit weakness. As a rule of thumb, the thickness of metal walls should always be higher than 0.8 mm. For plastic walls, the thickness should be higher than 1.5 mm.

Choosing the Right CAD Software

The vast application of CAD in manufacturing has led to the emergence of a lot of different CAD software for custom prototypes. While some of these are good, others can be unnecessarily complicated or can be too limited for certain applications.

Therefore, choose the correct CAD applications for your particular sector. A CAD software good for mechanical engineers and sheet metal forming might not be good for architecture, and vice versa. Find out the CAD software that fits your particular prototypes’ industries.

Creating a Checklist

It is crucial to have an initial checklist of the designs and features you want in the prototypes. It is easier to add features while designing the CAD file than to add features by modifying the file later.

Meterial Removed from Solid Block

Simplify Drawing

There are multiple ways to create a CAD design for the same prototype, and multiple ways to create the drawing for the CAD design. Keep drawings simple to reduce unnecessary machining steps. For complicated parts, it is a good idea to split the drawing into two different parts that can be joined later.

Rapid tooling: Injection molded prototypes via CNC machining

We have seen how CNC machining can be an excellent prototyping process. But machining can also be used indirectly to create injection molded prototypes.

By CNC machining tooling or molds, businesses are afforded a more cost-effective way of creating the apparatus required for injection molding. This CNC machined tooling can be created more quickly than traditional tooling, and is therefore a shortcut to molded prototypes. (For the final molded parts after the prototyping stage, traditional tooling methods may be employed.)

Using the rapid tooling process is much more cost-effective when ordering larger volumes of molded parts, since the machined tooling costs a lot more to fabricate than the molded resin parts themselves. And although large quantities may not be particularly desirable during the prototyping stage, the authentic molded prototypes will be more representative of a molded part than, for example, a 3D printed alternative.

Endnotes

For saving costs and avoiding long-term issues, prototypes are an integrated part of the manufacturing process. CNC machined prototypes are a great way to go ahead with the prototypes stage, providing fast and highly precise models.

Following the information provided in this article, it is possible to create high-quality prototypes. An important step is to use the tips provided for making perfect CAD design for rapid manufacturing, simple CNC machines, advanced CNC technology, or any other computer-aided manufacturing process.

If you require the perfect prototypes without investing in highly costly equipment and skilled labor, 3ERP provides CNC machined prototypes at your doorstep.

Frequently Asked Questions

Here are the answers to some common doubts that people face regarding CNC prototyping:

1. Is CNC machining the best option for prototyping?

CNC Prototyping machining is the best option for prototypes when the focus is on fast production, low tolerances, or material versatility. For low-budget and cost-effective prototyping using thermoplastic materials, 3D printing can be a viable option.

2. Which is cheaper: CNC machined prototypes or injection molding prototypes?

Due to the requirement of molds in injection molding, the lead cost of injection molding is higher than CNC machining. While in large-scale production the cost of molds splits over a huge volume, prototypes are small-volume production making injection molding the costlier option. Additionally, the cost of CNC prototype can be lowered by steps such as selling recyclable waste material which also lowers the environmental impact.

3. How much does CNC prototyping cost?

The cost of a CNC prototype can vary drastically based on the particular requirements of the prototypes. Generally, the cost starts at about $35 per hour for 3-axis machines and can go up to $120 per hour for higher certain axes machines. The certain axes required will depend on the complexity of the prototypes.


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