One of the most popular methods of processing various materials is milling. It involves shearing the coatings of the element until the desired shape is obtained. In this way, really complex structures are created - regardless of dimensions. However, it is worth knowing that milling of plastics proceeds differently than metals. Using the wrong method can lead to material damage. Therefore, we encourage you to familiarize yourself with the differences between metals and synthetics during machining.
What does the milling process involve?
As mentioned in the introduction, milling belongs to the methods of machining. It is based on the rotary motion of the milling cutters. The blades are moved along the material, which results in its cutting. Importantly, the tools remain in motion, while the object being machined remains stationary. This distinguishes milling of metal or plastics from turning, which requires the material to move around the lathe knives.
In this way, unnecessary layers of material are separated from the object. The freedom of cutting is almost unlimited. However, it should be remembered that the milling machine works primarily on flat surfaces. For irregularly shaped elements, it is better to use other machining methods.
Milling is done manually or automatically. The manual process is carried out in strictly defined situations, e.g. small-scale production. On the other hand, CNC machining of plastics is useful when unmatched precision and full repeatability of the process are required. Computer-controlled machines can produce identical products in thousands of copies. Therefore, automatic milling becomes a cheaper solution for implementing large-scale projects.
How is metal milling carried out?
We already know the general principle of conducting, so now it's time to look at the details. Milling in metal is done using ball mills adapted for working in metal. The plural form was used here for a reason. Metals are quite hard, so a single blade may simply not be able to cope with the task. So how many of them are needed? Usually two or three blades are used, which are placed on the cylindrical or frontal surface of the milling machine. They are set in rotary motion, which allows them to cut the material underneath. Mills are created using high-quality raw materials, such as high-speed steel (smaller models) or sintered carbides (larger models).
Metal processing is divided into concurrent and counter-current. The first of these involves - as the name suggests - concurrent motion, that is, consistent, cutting edge and material. Metal milling using this method begins by determining the starting point. The processing continues until the thickness of the cut material reaches the expected level. The biggest advantage of concurrent metal milling is that it does not harden the material, which is not insignificant for the life of the tools. Unfortunately, it also has one serious drawback. Namely, the force acting on the mill is very high, and the generated vibrations can lead to unwanted situations.
The situation is different in the case of the second method. Counter-current sheet milling is the opposite of concurrent. The mill moves in one direction and the processed material in the other. Over time, the edge is pressed more and more against the element, which results in the removal of excess. Of course, such a method of processing gives worse results than in the case of concurrent milling, but it remains very useful due to the reduction of vibrations and less force acting on the mill.
What to pay attention to when milling in metal?
There are several aspects to remember when processing sheets, regardless of the chosen method. First of all, due to their hardness, the milling cutter blades must work at increased power, which generates heat. If there is too much of it, it can damage the tools and the material. Therefore, sheet milling must use a special cooling system. It varies depending on the type of metal:
- Standard steel is dry milled using compressed air, which also removes chips;
- Heat-resistant alloys require cooling emulsion;
- Stainless steel and aluminum cannot do without coolant to reduce the risk of build-up;
- Cast iron requires a coolant to bind the dust generated by the process.
It should be noted that thin-walled elements and wet milling method require very intensive cooling due to the risk of deformation of the element.
What does the machining of plastics look like?
The rough machining of synthetics proceeds in a similar way to metals. Therefore, we will not repeat all the details here and will focus only on what really distinguishes the milling of plastics.
The method is implemented using milling machines, plotters, or multi-tasking CNC machines. Importantly, you can also use tools designed for milling in metal, especially soft ones, such as aluminum. However, one must be very careful during the process, so it is better to use them only when there is no other option. The machining of plastics is safer and more efficient with tools made of solid carbide (VHM). They have large chip channels for chip removal and surface cooling. End mills are most often used, which reduce vibrations. For composites, it is recommended to invest in tools with a diamond coating.
When it comes to choosing the method of milling - climb or conventional - experts recommend choosing conventional. This avoids the formation of burrs, i.e., the remaining part of the material on its surface or edge. This negatively affects the quality of the product. As for flat surfaces, it is recommended to use face milling, not cylindrical, due to efficiency.
What to pay attention to when milling plastics?
During machining, it is necessary to use high speeds in combination with medium feeds and a small angle of attack. Only in this way can a surface of good quality be achieved. The effects will be even better when using single-edged tools. When milling plastics, there is usually no need to attach more than two blades (in the case of harder synthetics).
The mounting of the element also proceeds in a slightly different way. You can use double-sided adhesive tape for this.
How much does sheet milling cost, and how much for plastic?
As one can easily guess, the differences occurring in both types of material, as well as the need to use slightly different methods and tools, enforce a difference in price. However, it is impossible to calculate a specific ratio of incurred costs, e.g. 2:1 for metals is the result of the influence of many factors on the cost estimate. Specialists dealing with the processing of plastics or metals take into account, among other things, the type of raw material, the size of the order, the type of project, or the need to carry out unusual work in exceptionally complex orders. Therefore, it is difficult to indicate what is more profitable.
The differences in price are therefore significant, but not so large as to be of greater importance. Fortunately, individual service pricing allows to reduce the expenses for project implementation. Especially when using CNC machines for mass production.
Summary of the most important differences
Now that everything is known about both materials, we can proceed to the summary. The processing of plastics differs in details from metal milling, although the general principle remains the same. The most important differences include:
- CNC milling of plastics generates large amounts of chips. Therefore, it is necessary to use advanced methods of contamination removal, such as industrial vacuum cleaners. In the case of metals, manual cleaning methods can suffice.
- On the other hand, milling in metal generates a large amount of heat. Therefore, an effective cooling system is needed. Otherwise, both the milling machine and the processed element will be damaged.
- Machining of plastics also cannot exceed a certain temperature, but instead of using a cooling system, it is enough to select the optimal parameters of the milling machine. They are determined individually for each type of material.
- Metals are hard, so single-blade machining, as in the case of plastics, is pointless. At least two knives on the front or cylindrical surface should be used to achieve the appropriate surface quality.
Proper selection of milling cutters and working temperatures, as well as skillful use of tools, is not possible without experience and special competencies in this field. Therefore, it is better to entrust the milling of materials or metals to professionals.
We invite you to contact us by phone or email to discuss the details of cooperation. We will be pleased to perform milling of metal and other materials at an attractive price.