Manufacturing started with the development of the first tool by humans. With time things got complicated and thus their manufacturing methods.
In this industrial age after several industrial evolutions, there is a greater emphasis on precise and accurate manufacturing of products. The precision manufacturing of products is only possible due to recent advancements in machines’ ability to deliver precision machining services.
Precision machining is now the backbone of our current manufacturing industry. Without this, there will be no smoothly running cars, fast-moving trains, or jets flying in our skies.
So what is precision machining and how to get precisely machined parts?
What is the Meaning of Precision Machining?
Precision machining is a term used to classify a machining process that produces products with highly accurate dimensions.
More technically speaking, a process that can machine a product or part whose final dimensions have a very tight tolerance. Tolerance is the maximum allowable or acceptable deviation from the required dimension.
For example, you design a shaft with a diameter of 10 millimeters. Now it’s not possible to manufacture an exact 10 mm shaft. So you need to mention tolerance or deviation from that 10 mm that is acceptable to you. For a very simple application, tolerance can be 0.1 mm means you can accept a shaft of any dimension between 9.9 mm to 10.1 mm in diameter (like 9.95 mm or 10.05mm).
Note: Tighter tolerance limit for any product, higher precision machining will be required to manufacture that product successfully.
Why is Precision Machining important?
You have a car that dries smoothly, you travel on a fast-moving train and you have passenger jets that can fly hundreds of kilometers at any time. These machines are capable of delivering their best because all their components fit and work together seamlessly. To fit parts of these super machines and to make them work perfectly, they need to be made so precisely that their final assembly has to be as precise as 100 parts of a millimeter or more.
So there are few people living in the world today and all the facilities we have using different machines are impossible without precision machining. Each and every product we have is not possible with precision machining.
Note: Even if the product itself does not need precision machining, the machines that manufacture that particular product do need precision machining.
What machines are used in Precision Machining?
Precision machining is all about the delivery of accurate and precise products that are machined within very tight tolerance limits. So in precision machining, there is no room for any human error. So precision machining cannot be done on any type of manually operated machine. It is always performed on a computer numerically controlled machine called CNC machine.
Note: It does not matter which type of machine or which operation you want to perform during your Precision machining task, it has to be a CNC machine.
Can all CNC machines deliver the same level of precision machining? No, different CNC machines deliver different levels of precision machining. It totally depends on the CNC machine’s ability to deliver a certain level of precision.
In the most simple terms, whenever a machine is being controlled by a computer for the manufacturing process, then it’s called a CNC machine. So all basic machines when controlled by computer will be called CNC machines.
Some of the most common machines used for precision machining are
1. CNC Machining Center
2. CNC Turning Center
3. CNC Wire Cut Electric Discharge Machine (EDM)
4. CNC Electric Discharge Die Sinking Machine
5. CNC Precision Grinding
All of the above mentioned machines can deliver you precision machining services but for each machine, it depends on several factors and their abilities to deliver precision machining.
Note: The same machine type that is developed by different manufacturers will have differences in their abilities to deliver precision manufacturing.
Which Machine Abilities Control Precision Machining?
As it has been mentioned precision machining is the machine’s ability to deliver accurate parts. So the question arises which machine abilities control the precision machining process?
For any machining process, the removal of material is obtained by relative movement of the cutting tool and workpiece against each other.
So to deliver precision machining the machine should be able to be precisely controlled.
a. Movement of cutting tool
b. Movement of workpiece
This precise control of movements of cutting tools and workpieces should be within the tolerance limit setup for precision machining.
For example, to do precision machining for a tolerance limit of 0.005 mm, a machine should be able to control the relative movement of the cutting tool and workpiece to 0.005 mm.
Note: For precision machining, the tool should be able to cut as per expectations without compromising the quality of the cut over time.
How Different Machines Work to Deliver Precision Machining?
As it has been mentioned precision machining is the machine’s ability to deliver accurate parts. So the question arises how different machines work to deliver precision machining
Well, the answer to that question is different for different types of machines. Turning center working is different from the machining center and similarly machining center is different from EMD. So we will discuss each separately.
CNC Machining Center
The machining center works by rotating the cutting tools and giving feed to its workpiece So for precision machining it is important to have very precise control on\
1. Cutting tool rotation
2. Workpiece feed
3. Tool quality/life
CNC machining centers are designed to cut 2D profiles on the workpiece surface with a given depth of cut for each profile. Depending on the quality of cutting tools and spindle speed, this machine can process materials like aluminum & its alloy, steel & alloy steel, and also some hard materials like titanium.
CNC Turning Center
The turning center works by rotating the workpiece and giving feed to its cutting tool. So precision machining depends on
1. Cutting tool feed
2. Workpiece rotation
3. Cutting tool quality/life
Like the machining center, it also cuts 2D profiles but only on cylindrical workpieces and can process all conventionally used soft to hard materials.
Note: In the world of precision machining CNC turning center and CNC machining center are the most used machines for all types of conventional work with tolerance limit of about 0.01 mm.
CNC Wire Cut Electric Discharge Machine
Wire cut edm uses a tungsten wire and electric current to remove material from the workpiece. Wire moves linearly throughout the workpiece thickness while the workpiece moves as per the input 2D profile.
So for precision machining, a highly precise control on the following is needed.
1. Wire speed
2. Wire diameter
3. Current intensity
4. Workpiece movement
CNC wire cut is a non-conventional machine (as cutting is done by electric current, not wire) and it has the ability to deliver exceptional quality precision machining. It can process hard to very hard materials. The tolerance limit of this machine can be between 0.001 to 0.005 mm.
CNC Electric Discharge Die Sinking Machine
Like wire cut, die sinking edm also uses electric current for machining. It uses a tool instead of wire and its tool moves only in an up-and-down direction whereas feed is given on a workpiece.
So for precision machining, a highly precise control on the following is needed.
1. Tool movement
2. Tool Shape
3. Current intensity
4. Workpiece movement
During die sinking tools must be able to maintain their shape to deliver quality precision machining. It can also process any type of hard to extra hard material. The general tolerance limit for this machine is about 0.025 mm.
Precision Grinding
There are a variety of precision grinding machines available including electric discharge grinding. Precision grinding working is all the same as normal grinding and the only difference lies in that different grinding wheels are specifically designed for different jobs.
So for precision machining, a highly precise control on the following is needed.
1. Type of Abrasive
2. Quality of Wheel
3. Wheel Rotation
4. Wheel linear movement
5. Current intensity (only for edm grinding)
6. Workpiece movement
Precision grinding can achieve a tolerance limit of 0.0013 mm for diameter and 0.00025 mm for round surfaces. EDM grinding has the ability to easily deliver precision of up to 0.005 mm.
Note: Precision Grinding is mostly used as a post-process with all other precision machining when other machines are not able to achieve the required tolerance limit.
How to Choose the Right Machine for Precision Machining?
The following factors must be considered while working on the point, what machine should you use for precision machining.
1. Shape
2. Material
3. Tolerance limit
Shape or Geometry of a Part
The shape of a part is among the things you need to consider as it limits your selection of machines. Shape not only limits the types of machine needed to do the job, it also defines the machine’s abilities needed to process that shape.
For example, selecting between a turning center and a machining center or between a three-axis machining center or a five-axis machining center depends on the shape needed to be machined during precision machining.
Material to be machined
The material from which part will be machined is very important as certain machines can only process certain materials. During precision machining, material hardness is very important as it defines the material machinability.
Hardness in simple terms is how hard it is to indent or penetrate cutting tool tips inside the material. Machinability is how easy or hard it is to machine and remove material from a workpiece.
For machines like the turning center and machining center, the material defines the cutting tools needed with the machine. Materials like steel and aluminum can be machined using high-speed steel tools but materials like titanium can only be machined using special carbide tools.
In machines like wire edm and die sinking, it’s about machines’ ability to cut through the machines. Here cutting tools are an integral part of the machine and usually made of very hard material, like in wire edm, it’s wire is made of tungsten
Tolerance Limit of the Product
The tolerance limit is the most important and critical factor in a precision machining job. The tolerance limit totally depends on the machine and cutting tools’ abilities to cut the material precisely. If your machine can process the shape and can also machine the material but it can not achieve the required tolerance limit, then you cannot deliver a precision machining job on that machine.
Steps Involved in Precision Machining
CNC machines used for precision machining follow the same pattern as off-normal CNC machining. Following are the steps involved in precision machining of parts.
Developing CAD Model
As CNC machines are controlled by computers and users need to tell the computer that to manufacture it, First a computer-aided design CAD model of the part is made.
Conversion to CAM
CNC machines cannot read CAD files so computers have to convert that CAD files into computer-aided manufacturing CAM files. In simple words in G and M codes for CNC machines.
CNC Machine Setup
The CAM file is exported to the machine and the CNC machine is then set up for the process. Loading workpieces, tools, and coolant and setting up any jig or fixture is part of the machine setup.
Execution
As the setup is complete, the machine can now be started and it will deliver the parts as programmed in the CAM file. This execution can be achieved in two or more steps if precision is not achieved in the first step.
How to Inspect Precision Machined Parts?
After the parts have been machined, they should be inspected for all the requirements that were initially set like dimensional accuracy, and surface finish. Just like precision machining the precision inspection of parts is a sensitive task and needs complete care for an accurate result.
Regular measurement-taking tools like vernier calipers, and micrometers can check the precision of parts up to 0.05 and 0.01 mm but for higher precision they fail. For high-precision applications tools like comparators are used. Electrical comparators and optical comparators are some of the highest precision inspection instruments in this regard. They have a least count of 0.001 mm.
One problem with the above tools is that they are for small parts. If a precision machined part is of few feet then it can only be properly inspected using a coordinate measuring machine CMM.
These CMM are all CNC machines and their efficiency is unmatchable in this regard. CMM can easily measure precision up to a micron level. They are also able to monitor and inspect the surface finish of the finished part.
Last Words
Precision machining is all about machining a very tight tolerance part and precision machining depends totally on machine and machine alone. If your primary process is not able to deliver the required tolerance then, secondary processes like precision grinding can be used.
Kinsai is the top name of Precision Machining Services in China. We have 15 years of manufacturing metal parts and implementing a range of key methods including:
1. Precision CNC Machining
2. Precision Grinding
3. Wire EDM Machining
4. Casting
5. Welding and Drilling
We accumulated rich experience in manufacturing high-quality and high-precision CNC machined parts for customers all over the world. If you are looking for precision machining services, welcome to contact us for further discussion and a quote.
Mr. Alex Yan.
Sales Manager of Kinsai.
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