CNC machined parts require clever design and detailed analysis for professional results.

Are the dimensions of the part pattern suitable for the characteristics of the CNC machining process?

• Are the geometric elements of the contour pattern sufficient for accurate machining?
• How reliable is the positioning reference?
• Can the machining accuracy and dimensional tolerance for the part be guaranteed?

For part blanks, a separate technical analysis is also required, with the following two steps being critical:

• Analyze the suitability of the blank in terms of installation positioning and the size and uniformity of the margin
• Determine whether the machining allowance of the blank is sufficient and whether the remaining amount is stable during mass production

KICastings provides access to a wide range of materials for CNC machining, along with a friendly consultation service. All parts are manufactured using a highly automated process in order to improve production rates and accuracy. Although our precision stainless steel castings exceed industry standards, we offer CNC machining for specialty shapes and dimensions.

The CNC machining process

The overall machining process is dependent on multiple factors, with the right tools and technologies needed to ensure processing precision and quality outcomes.

1. Computer Aided Design (CAD)
CAD is the first step in the machining process, with decisions made during this phase affecting every aspect of production. Software tools and methods are an important part of the component design because they allow manufacturers to create an accurate picture based on component measurements and specifications.

Machining tools and real-world complications can restrict geometries and affect design decisions. CAD technology gives people the ability to identify problems and make changes in the virtual world before they invest heavily in the production process.

2. Machine tool selection
Different parts need to be machined with different CNC machines, with the material, type, and size of the component influencing the machining process. CNC machines should always be selected according to the specific design requirements of the part.

It’s important to identify all processes and steps before production begins, with each machine needing to be built and set up according to the project in question. A number of CNC operations can be performed if required:

• CNC drilling – This process utilizes drill bits with multiple points to produce holes in the surface. These holes can be aligned with complete accuracy, with drill bits also able to perform reaming, countersinking, and counterboring operations.
• CNC milling – When a rotating cutting tool is used to remove material, the process is called milling. This task is able to produce rounded and smooth surfaces along with deep holes, threads, and slots.
• CNC turning – When a lathe or other tool is driven into the workpiece in a repeated linear fashion, the material is removed from the outside of the part and cylindrical shape can be created.

3. Select the tool point and tool change point
Once the tools have been chosen and set up to meet the demands of the project at hand, it’s important to select the tool point and tool change point. In programming, the workpiece is considered to be stationary while the tool is moving.

Usually, the tool point is referred to as the program origin. When making your selection, it’s important to choose tool points that are easy to find and easy to program. Other critical factors include the minimization of tool error, and the ability to access easy and reliable inspection procedures.

• Tool point – For accurate index control machining, this is the starting point for tool movement relative to the workpiece.
• Tool change point – A change point also needs to be set when you’re working with machine tool programmings such as a machining center or CNC lathe.

4. Processing plan and methods
The selection of a processing plan with definable methods is needed to ensure processing precision. When making a selection, all methods should be considered in relation to the shape, size, and heat treatment requirements of the part being machined. All processing methods should be initially determined based on the material, the intended accuracy of the part, and the roughness requirements of the main surface.

5. Selection of machining allowance
Machining allowance refers to the difference between the physical size of the blank and the actual size of the part. This allowance can have a significant impact on accuracy, costs, and timelines, so it’s important to get it right. There are two primary principles for the selection of machining allowances: the principle of minimum machining allowance and the principal of sufficient machining allowance. Having an adequate margin is increasingly important as the machining process proceeds, and is often defined based on the requirements of the final step.

6. Determination of the cutting amount
Determining accurate cutting amounts is important to ensure the final accuracy of the machined component. Cutting quantities include depth of cut, spindle speed, and feed rate.

• The depth of cut is determined by the rigidity of the machine tool, fixture, tool, and workpiece.
• The spindle speed is determined by the allowable cutting speed.
• The feed rate is determined by the machining accuracy and surface roughness requirements of the part, along with the material properties of the workpiece.

7. Inspection and testing
When parts have been machined, they need to be inspected for faults and tested for accuracy. This is particularly important during the initial days of production, with issues ironed out early in the process leading to significant cost savings down the road. From design to inspection, CNC machining is a multi-pronged process that requires a diverse skill set and lots of industry experience.