CNC Milling: Sungplastic’s CNC Milling Center For You

Using multipoint, computerized cutting tools, a workpiece is cut during the CNC milling process. The procedure, which is well-known for its accuracy and precision, is essential to many industries, the most prominent ones being the automotive and aerospace sectors.

Before selecting CNC milling for your project, read our explanation of all the things you should know about it.

What is CNC Milling?

CNC milling is a computer-controlled machining process that utilizes a cutting tool to selectively remove material from a workpiece. The fundamental setup involves positioning the workpiece on the machine’s table, while the cutting tool, affixed to the spindle, undergoes rotation and movement to shape the workpiece into its final form.

The precise rotation and motion of the cutting tool are contingent on the type and sophistication level of the CNC milling machine. This process is exceptionally versatile, accommodating a wide range of materials, including aluminum, plastics, wood, and glass.

CNC milled parts exhibit high tolerance, as milling machines can achieve precision within a range of +/- 0.001 in. to +/- 0.005 in. (with some machines capable of reaching an impressive tolerance of +/- 0.0005 in.).

How Does CNC Milling Operate?

CNC milling, a fundamental aspect of the CNC machining process alongside drilling and turning, distinguishes itself through its unique mechanism. The process revolves around the removal of material from a workpiece using a computer-controlled cylindrical cutting tool that rotates and moves along multiple axes.
Key Steps in the CNC Milling Process:

Step 1: Preparation of a 2D or 3D CAD Model

Utilize CAD/CAM software, such as Autodesk Inventor or SolidWorks, to craft a machinable 2D/3D representation of the final product. The CAD file creation may involve converting 2D images into 3D CAD files or tracing a 2D image to transform it into a 3D file. Additionally, a technical drawing is provided to the operator, encompassing critical features, dimensions, tolerances, thread indications, finishing preferences, and construction lines.

Step 2: Exporting the Design to a CNC-Compatible File Format

To enable comprehension by the CNC milling machine, the CAD model must be exported into CNC-compatible file formats, such as STEP and STL. CAD/CAM software facilitates this conversion. If needed, online services like Cadexchanger and Convert.emachineshop.com can assist in converting designs to the requisite format. The resulting file guides the machine in rotational and linear movements, cutting sequences, toolpaths, and the associated speeds of the machine and workpiece.

Step 3: CNC Milling Machine Setup and Operation

The operator affixes cutting tools to the spindle and positions the workpiece on the table. Subsequently, the machine is set up to execute the machining program, initiating the milling process. This involves executing the predefined toolpath, ensuring precise rotational and linear movements, and regulating the speed of both the machine and the workpiece.

Types of CNC Milling Operations

CNC milling encompasses various operations, each distinguished by specific setups and applications. Here are common types of CNC milling operations:

Face Milling

In face milling, the rotating axis of the cutting tool (face milling cutter) is perpendicular to the workpiece surface. This cutter features interchangeable inserts, employing multiple cutting teeth to deliver a cutting action that results in higher-quality surface finishing. The process is closely controlled, facilitating the production of desired surfaces with ease.

Plain Milling

Plain milling is a column and knee operation designed for milling plain horizontal surfaces. The cutting tool lies parallel to the workpiece, allowing cutting from one end to the other. Longitudinal, cross, or vertical feeding of the table is possible for operators.

Angular Milling

Angular milling involves milling flat surfaces at an angle, similar to plain milling but with an angular setup. Two types of angular milling cutters exist: single angle and double angle. Single-angle cutters, suitable for 45° or 60° angles, feature teeth on the cutter’s angular face. Double angular milling cutters, with V-shaped teeth, are preferable for milling flat surfaces at 45°, 60°, and 90° angles.

Form Milling

Form milling is employed for creating irregular contours on a workpiece, which can be curved or combined with straight lines. The cutter’s teeth correspond to the shapes of the desired contours, either concave or convex. For instance, a form milling cutter with a convex edge is used to create a product with a concave edge. Although slightly slower (about 20 to 30%) than regular milling, form milling is effective for intricate cutting to produce curved surfaces.

Other Types

• Slot Milling:
  Used to make a slot in the workpiece, with the cutter’s width smaller than the workpiece width.
• Side Milling:
  Suitable for producing a flat vertical surface in the workpiece, with depth controlled by rotating the vertical feed screw of the table.
• Gang Milling:
  Involves using two cutting tools on the same arbor to cut horizontal surfaces, offering unlimited potential and reducing milling process time.

Material Selection for CNC Milling

Selecting the appropriate materials for CNC milling can be a complex task given the vast array of options available.

Consider the following factors along with some common materials:

Part Functions:
The chosen material should possess inherent properties that align with its intended functions in the specific usage environment.
Example: Stainless steel, with superior corrosion resistance, is preferable over carbon steel in corrosive environments.

Stress Load:
Materials for parts subjected to high stress should exhibit stability under stress to prevent deformity or cracking.

Dimensional Tolerance:
Material selection influences dimensional tolerance, impacting the accuracy of milling and facilitating ease of assembly.

Operating Temperature:
The melting temperature of the material should be below the operating temperature of the CNC milling machine to avoid deformation during milling.

Cost:
Cost is a crucial factor in material selection, but it’s essential to balance budget considerations with choosing a material that offers optimal mechanical properties.

Common Materials for CNC Milling:

• Metals: Aluminum, Stainless steel, Tool steel, Mild steel, Brass, Copper.
• Plastics: ABS, Polycarbonate, Nylon…
• Others: Ceramics, Composites, Phenolics.

Each material category has its unique properties, making it suitable for specific applications. Careful consideration of these factors ensures the selection of materials that align with the requirements of the CNC milling process and the intended functionality of the finished parts.

Advantages and Disadvantages of CNC Milling in the Production Process

CNC milling plays a crucial role in various industrial production processes, offering distinct advantages while also presenting some drawbacks. Here are a few advantages and disadvantages associated with this manufacturing method:

Advantages

Accuracy and Precision:
CNC milling machines exhibit higher levels of accuracy and precision, enabling the creation of parts according to precise technical specifications. Tolerances as tight as 0.0004 can be achieved, and the automated nature of the process minimizes the likelihood of human errors.

Fast and Efficient:
In comparison to conventional milling methods, CNC milling machines are known for their speed and efficiency. The capability to accommodate multiple cutting tools (depending on the Automatic Tool Changer, ATC) facilitates effective tool-changing, contributing to an efficient overall process.

Large Compatible Material Range:
CNC milling is compatible with a wide range of materials, including plastics, composites, and metals. This versatility makes it an ideal choice when working with various materials, particularly when starting with a block of raw material.

Disadvantages

Material Wastage:
As a subtractive process, CNC milling involves the removal of material to shape the desired part. This results in a significant amount of material wastage, particularly when compared to manufacturing methods like 3D printing services that are additive in nature.

High Level of Maintenance:
CNC milling machines require a substantial level of maintenance to ensure optimal functionality. Given the considerable expense associated with these machines, ongoing maintenance is crucial to preserving their performance and longevity.

Applications of CNC Milling Technique

CNC milling, known for its accuracy, precision, and high tolerance, finds extensive use across diverse industries. Below are some of its notable industrial applications:

Aerospace

CNC milling is instrumental in crafting various aeronautic components using lightweight and durable materials like Titanium and Aluminum. The need for exceptional accuracy and precision makes CNC milling well-suited for the stringent requirements of the aerospace industry.

Automotive

In the automotive sector, CNC milling is employed to achieve efficient production without compromising accuracy. The process is applied in crafting various automotive components, including interior panels, cylinder heads, drive axles, suspension components, exhaust parts, and gearboxes.

Agriculture

CNC milling is suitable for producing general-purpose parts and components essential in agriculture, such as gears, shafts, nuts, bolts, and flanges. Its adaptability caters to both large-scale and short-term production needs within the agricultural sector.

Medical

Precision and unique designs are paramount in medical applications, especially for parts like prostheses. CNC milling emerges as the preferred method for crafting such intricate medical components, ensuring the retention of precise designs and contributing to productivity and efficiency in the medical field.

How Much Does CNC Milling Cost?

The cost of CNC milling is influenced by several factors, including material costs, design intricacy, and machine specifications. Here is a brief analysis of these factors and their impact on costs:

Part Design

Designing the part constitutes a significant expense. Whether outsourcing the CAD file creation to a designer or undertaking it in-house, costs can accrue. Additionally, the involvement of a manufacturing engineer to verify the part and a programmer to convert the CAD file into a CAM file adds to the overall cost. Many CNC milling services include these costs in their quoting platforms.

Design Complexity

The complexity of a product design necessitates a milling machine that can effectively handle intricate designs. Greater complexity often requires a more sophisticated milling machine, resulting in higher costs. Complex designs also extend production time, impacting costs as CNC milling services typically charge on an hourly basis. For companies using their CNC millers, increased machine power consumption contributes to additional costs.

Production Volume

Outsourcing to CNC milling services for large orders is generally more cost-effective than smaller orders, thanks to economies of scale. The cost per milled item decreases with larger orders. CNC milling’s high repeatability reduces production time, further contributing to cost efficiency.

CNC Milling Machines

Various types of CNC milling machines exist, each characterized by distinct attributes and associated costs. The primary determinant for selecting a machine type is the complexity of the design, as discussed earlier.

CNC milling services typically establish machine costs on an hourly basis, sometimes including the operator’s cost. This calculation considers the machine’s purchase cost and its expected annual operating hours. For instance, in Europe, 3-axis machines are priced at approximately $40 per hour, while 4-axis and 5-axis machines range from $75 to $120 per hour.

However, alternative options, such as Chinese CNC milling services, may offer more cost-effective solutions in certain situations.

Material

Material cost is a significant factor influenced by factors like availability, market cost, and machinability. The cost is typically per block, and there are two major types of CNC materials: plastics and metals.

Plastics: Plastic materials, such as ABS ($17), Delrin ($27), and Nylon 6 ($30), are economical, highly machinable, and readily available, resulting in lower material costs.

Metals: Metal materials, like Aluminum 6061 ($25), Aluminum 7075 ($80), and Stainless Steel 304 ($90) per block, are generally costlier than plastics.

Surface Finishing Options

Additional surface finishing options, like anodizing and powder coating, can enhance the aesthetics of the part or conceal signs of CNC milling. However, these options contribute to an increase in CNC milling costs.

Additional Completion Costs

Shipping costs are an additional factor affecting overall CNC milling expenses. The shipping cost is contingent on factors such as distance from the CNC milling service, deadline requirements, and the weight of the materials.

These factors collectively shape the CNC milling cost and should be carefully considered when formulating a budget. If uncertainties persist regarding cost calculations, consulting with experts or obtaining an instant quote from CNC machining services is recommended.

Types of CNC Milling Machines

A milling machine consists of various components that cut workpieces, and different types of milling machines offer unique setups for various operations. Here are common types to consider for your project:

Vertical Milling Machine

The vertical milling machine is a 3-axis machine with a table and arm connected to a vertical column, and the spindle is also vertical.

Regarding the arm, the table moves up and down the z-axis.

Concerning the spindle, the table’s movement depends on the type of vertical milling machine. For instance, in a turret vertical mill, the spindle is stationary, and the table moves along the x-axis. In a bed vertical mill, the table moves on the x-axis, and the spindle moves along the arm on the y-axis.

Suitable for complex operations due to accuracy, especially for vertical surfaces and angular shapes.

Horizontal Milling Machine

Horizontal milling machines, similar to vertical ones, can rotate along the z-axis in the case of universal machines, making them 4-axis milling machines.

These machines have a spindle with a horizontal orientation and are less versatile but more suitable for heavy machining.

Multi-Axis CNC Milling Machine

Multi-axis CNC milling machines can cut at different angles and move along various axes. Different kinds include:

• 2-axis milling machines:
  Work in the x and z axes, cutting vertically and horizontally in one direction—simplest type of CNC millers.
• 3-axis milling machines:
  Move in the x, y, and z axes, cutting workpieces vertically in any direction—most common type but has limitations on cutting complex parts uniformly.
• 4-axis milling machines:
  Spindle can travel along three axes without the workpiece moving, and it can also rotate along the X-axis or A-axis—suitable for complex milling operations.
• 5-axis CNC milling machines:
  Spindle and cutting tool move along three axes and allow rotation along two axes (x-axis, y-axis, or z-axis)—most complete multi-axis CNC machine, capable of working on several parts.

These different types of milling machines cater to a range of machining needs, offering flexibility and precision for various projects.

Components of CNC Milling Machine

A CNC milling machine consists of various components, each serving a distinct function to facilitate the cutting action. While the design and sophistication of these components may vary among CNC millers, their fundamental functions remain consistent. Here are the general components commonly found in these machines:

Frame

The frame provides stability and rigidity to the machine. It encompasses components such as the base, detachable columns, and the headstock, which houses the spindle.

Spindle

The spindle constitutes the entire rotating unit of the milling machine, comprising the shaft that holds the cutting tools and other integral parts. Its orientation can be either horizontal or vertical, depending on the specific milling machine. A motor, guided by the CNC controller, rotates the spindle along the designated axis.

Axes

The primary axes include x (vertical), y (horizontal), and z (depth). Some machines may feature additional rotating axes denoted as A, B, and C. The sophistication of the machine determines the capability to rotate along these axes. For instance, 4-axis CNC milling machines can rotate on the A-axis, while 5-axis machines can rotate on the A and C axes or B and C axes.

Columns

The columns rest on the base, which houses a coolant reservoir and pump, playing a crucial role in supporting the machine’s cooling system during the cutting process. The column’s configuration may be single or vary depending on the complexity of the machine.

CNC Control Panel

The CNC control panel includes a monitor and programming buttons for inputting data and codes. Serving as the nerve center of the machine, it controls and oversees the milling process, ensuring precision and accuracy in the operations.

Automatic Tool Changer (ATC)

The Automatic Tool Changer (ATC) plays a crucial role in facilitating tool changes during the milling process, thereby enhancing the machine’s speed, tool-carrying capacity, and overall productivity.

There are two main types of ATC:

• Drum ATC: Suitable for milling applications requiring fewer than 30 tools.
• Chain ATC: Suitable for milling applications requiring more than 30 tools. These can be either mounted at the column or separately attached to the machine.

The distinction between these types is generally based on the number of tools required, though variations may exist depending on the specific design and manufacturer of the milling machine.

Tool Holders

Tool holders are instrumental in securing cutting tools to the CNC machine. There are various designs and sizes, with three major types of tool holders being BT, CAT, and HSK.

• BT Tool Holders:
  Standard-sized tool holders with a robust design and a retention knob featuring metric threading.
• BBT Tool Holders:
  Upgraded BT tool holders with double contact points with the spindle, enhancing stability and rigidity. Highly recommended in the CNC milling space.
• HSK Tool Holders (Hollow Taper Shank):
  European-designed tool holders sharing the same angle as BT tool holders but featuring an additional orientation groove at the flanges. Suitable for high-speed machining with low tolerance.

Table

The table serves as the solid base for placing the workpiece and securing it using fixtures or a vice. The type of tables and their additional functions depend on the machine. For example, some tables incorporate T-slots for easy clamping, while horizontal CNC millers may utilize Tap-holes pallets for enhanced flexibility.

Coolant Tank

The coolant tank contains a coolant supplied to the cutting surface or the spindle during milling. As milling generates heat, the coolant helps cool the surface, prolonging the machine’s lifespan. Coolant tanks come in various sizes, and the optimal choice should be tailored to the specific machining operation.

Complete CNC Machining Services at Sungplastic

With an emphasis on producing quality metal and plastic parts with high tolerance at a reasonable price, we offer expert CNC machining services. Our in-house, state-of-the-art multi-axis CNC milling equipment in our self-owned factories enables us to provide you with high-quality parts on short lead times. At the same time, we supply CNC turning manufacturing. For metal parts or plastic prototypes, we have rich manufacturing experience。

If you are looking for a CNC machining manufacturer, including CNC milling, CNC turning, EDM, etc., whether small-scale or high-volume production, we are the best for you.