Metal Machining

Machining is a process of manufacturing metal parts by removing material from the initial stock using a hardened and sharpened tool. Almost any manufacturing process involves some degree of machining. The reason for that is the precision and quality that metal cutting provides. There exists no other method of manufacturing parts that makes more precise and finer products as machining. That is why there are tens of variations of metal removal methods, thousands of machining tool modifications and millions of enterprises that implement machining all over the world.

Machining Specifics Depending on the Product Quantity

Manufacturing processes differ greatly depending on the number of parts that need to be produced because the proportions in manufacturing costs when making one part and a million parts are completely different.

When you need to make a small number of parts per year, you do not really care about material ratio. You can waste more material because you don’t have to buy much for a small number of parts anyway. What you really care about, is the need to buy any special fixtures or tools or even a whole machine tool and you try to avoid it, if possible because buying a whole piece of equipment just for one or two parts is irrational. You try to use standard fixtures and standard tools to minimize the costs. You can also spend more time preparing and machining the part and you don’t need to optimize the technology since you don’t need to produce many parts anyway and the time saved producing one or two parts is not that big compared to mass production as you will see later. Such manufacturing situation is characteristic for prototyping.

When manufacturing a large set of parts, the picture is completely different. Every gram of excess waste can play a large role in the total cost of each part. That is why manufacturers tend to optimize material ratio as much as they can. They do it by buying specialized or special equipment because it will be guaranteed to be used a lot and its price when divided for a number of parts will be minuscule. Producing a large number of parts takes a lot of time. That is why optimizing manufacturing technology of the part is so important. One second of saved time for one part is multiplied by the number of parts can give days or weeks of spare time.

Now, the last type of production is the most widespread nowadays. It is the medium-size lot production. In this case, a medium number of parts is produced and is then change by another medium-sized set of other parts. In this case, flexibility is the most important factor. Lead time is decreased through the use of standardized fixtures that can be combined into a required structure and through the use of automation of manufacturing process design. CAM systems and CNC machine tools are widely used in such a manufacturing situation.

The Most Common Machining Methods

The most widely used machining operations are milling and turning. Those two methods compose up to 80% of all machining volume. They allow manufacturers to create almost any form of surface with the highest precision while using almost any industrial material. The first method involves fixing a part on the machining tool and cutting it using a revolving milling cutter. Milling cutters can be different shapes and sizes and can be oriented in different ways and have different degrees of freedom while cutting the stock but the main principle is that the part is fixed and the tool revolves and moves to cut it.

Turning uses a different principle. Here, the stock revolves and the tool can only move in linearly. Modern CNC lathes have a lot of additional features where additional mills and drills are implemented to make special holes and planes under different angle toward the revolving axis.

If a high precision and a fine surface finish is required, using abrasive methods is absolutely necessary. The difference of those methods compared to the previous ones is that abrasive methods use hard grains imbedded into a softer connecting material to “scratch” the part until it is finished. That way, only a small fraction of material is deleted by each grain and the cuts are very small, so the precision and surface is much better. By using abrasive cutting, tolerances up to IT5 and surface finish up to Ra 0,16 is possible. Well, even finer results are achievable but they depend on the material and conditions.

Some innovative machining methods have been developed in recent decades. They include Electrical Discharge Machining and Electro-Chemical Machining. Both of those processes are defined by the fact that they do not depend on the hardness and strength. EDM technology involves the condenser effect. As electrical current is provided to the stock and the tool with an insulator between them, when discharges happen, some fraction of stock material is evaporated. The second method bases on electrolysis, where the stock, being the anode, is dissolved as a result of chemical reaction between the stock and the tool in a conducting liquid.

The Problem of Choosing Industrial Metals

Modern industry can offer over 300 different steel alloys, and tens of aluminum, bronze, magnesium, copper, titanium and other alloys. Even alloys of one element are machined differently and yield different results when end-product is considered. This brings about a large problem of choosing the right material for the part. In this case, designer should take into account the machinability of the material. For example, titanium alloys have great performance qualities but cutting it is very hard and expensive. That is why choosing a softer material of a different element will considerably decrease the manufacturing time and the part may not even lose in performance at all. That depends on the purpose of the part.

Conclusions

Machining is a method that is absolutely necessary in modern day manufacturing of any type. However, to minimize the time and cost of machining, certain things must be taken into account at the designing stage. Those things are the required number of parts, their material, the requirement for special tools or fixtures, the deadline for manufacturing. Having taken at least some of those factors into account during the initial design stage, a considerable decrease in lead time can be achieved.