For securing the workpieces, CNC fixtures should be installed when processing them on machine tools. To assemble the workpiece is to determine where it should be positioned correctly with respect to the tool in a machine tool. If clamping of a workpiece is not done properly, it will affect directly on the accuracy of CNC machining for that part. In this article we will describe various types of CNC fixtures their design principles and applications.
What is CNC fixture?
CNC fixture refers to any additional devices used on machine tools during mechanical manufacturing processes which serve to secure a processing object in such a way that it takes up an appropriate position for processing or inspection and meets process requirements. It is often called fixture. Fixtures are designed to ensure accurate positioning as well as stability of workpieces throughout machining operations.
Most common materials employed for making CNC fixtures
The most common materials employed for making CNC fixtures are:
Steel
Steel can be used in making robust jigs having good stiffness like high strength steel or stainless steels which can bear heavy loads frequently while still giving stable gripping and supporting.
Aluminium Alloy
Aluminium alloys possess good machinability properties coupled with light weight features hence they find wide application areas when constructing tailored tools; They also offer enough strength and rigidity required by fixturing systems but at reduced weight thus making them easier to handle during setup procedures.
Composite Materials
Composite materials combine different advantages brought about by using various constituents within one structure so that carbon fiber reinforced composites have high strengths together with lightweight characteristics. These may be utilized in aerospace industry among others where performance levels need to match specific requirements.
Plastics
Plastics such as polyurethane, nylon etc., may be used when making lightweight holders or those which do not demand much rigidity due to wear resistance properties exhibited by these substances plus chemical stability considerations under certain working conditions.
Titanium Alloy
Titanium alloys exhibit outstanding corrosion resistance properties combined with high strengths thus enabling their use as special environment fixture materials for example within aerospace or medical devices applications.
When selecting materials for a fixture, it is important to take into account factors like workpiece material, process requirements, working conditions and cost so that the chosen material provides stable reliable clamping and support functions.
Types of CNC Fixtures
Machine tool fixtures come in many shapes with different names. They are usually classified by some attribute for convenience of design, production and management.
Classification by general features of fixtures
According to this classification method, there are five types of clamps often used: general fixture, special fixture, adjustable fixture, combination fixture and automatic line fixture. It shows the common features of different production type’s fixtures so that it is the main basis for selecting a fixture.
General Fixture
General fixture means that its structure and size have been normalized with certain versatility, such as three-jaw self-centering chuck; four-jaw single-acting chuck; bench vise; universal dividing head; center frame; electromagnetic chuck, etc..
It has wide applicability which can clamp various workpieces within a certain range of shape without adjustment or slight adjustment.
Using this kind of fixture can shorten the preparation period for production and reduce number kinds of fixtures thus lower down cost. The accuracy during processing on it is not high while productivity is also low and complex shaped workpiece can’t be held tightly so that it suits single piece and small batch production.
Special Fixture
Special fixture refers to those designed produced according specific requirements for machining process of given workpiece only.
Its characteristics lie in strong pertinence but no universality. In large-batch stable product manufacturing enterprises many different special fixtures are needed which could make higher productivity realized together with better finishing precision.
The design cycle manufacturing time consumed by special fixturing long because adaptability economy these devices have been facing challenges under conditions modern multi-variety medium-batch production.
Adjustable fixtures
Adjustable fixture is new in order to overcome the common clamp and special clamp deficiencies; and it changes only single locating element and clamping element on original fixture for different types and sizes of workpieces.
Group of fixtures
It is a fixture based on group process technology which aims at a group of parts with similar shapes. It is also called universal basic parts combined with replaceable adjustable elements, which have the same appearance as adjustable clamps but have more definite using objects, scientific design concepts, reasonable structures and easy adjustments than those.
Combination Fixture
Combination clamp refers to modular clamp which has been commercialized. Standard modular components possess high accuracy and wear resistance, can be assembled into various fixtures; after being used the fixture can be disassembled, leaving new fixtures to be built.
The use of combination fixtures can shorten production preparation time, save component reuse times and reduce number of special fixtures. Therefore when dealing with single-piece small batch multi-variety production or CNC processing, combined fixture is considered as a more economical one.
Automatic Line Fixture
Automatic line fixtures usually are fixed type (similar to special fixtures) or movable type (which moves along with workpiece during use and carries workpiece from one station to next along automatic line workstation for processing).
Classification by means of machine tools for fixtures
Milling Fixtures
These are usually linked with milling machines and are made to stabilize the workpiece during high-speed milling operations that allow complex cutting paths.
Turning Fixtures
Used in lathes, these are designed to hold the workpiece securely as it rotates so as to enable accuracy in cutting various shapes like cylinders.
Grinding Fixtures
Made specifically for grinding processes where it holds on firmly onto the item being worked on while also ensuring rigidity and precision required for surface finishes.
Welding Fixtures
These types of fixtures were created with an aim of keeping parts still relative to one another during welding hence preventing dimensional changes due to heat.
Designing for CNC Fixtures
To have the desired level of effectiveness and efficiency, there are certain things which should be taken into account when it comes to designing CNC fixtures.
- Accuracy and Precision
One of the main aims of having CNC fixtures is to hold workpieces securely in position during machining process so that they can be machined with required accuracy.
- Accessibility
Workflow can be made faster and manual handling reduced by creating easily reachable areas on fixtures alongside other ergonomic features.
- Modularity and Versatility
Flexibility can be improved if one designs modular type of fixtures that can take different sizes or geometries of workpieces hence making them adjustable enough to accommodate any kind or shape of a workpiece.
- Rigidity and Stability
Any design for fixture meant to be used in CNC machining should take into account rigidity since such machines produce high cutting forces as well as vibration forces which may cause inaccuracy if not controlled properly; therefore it must withstand this dynamic load without bending or twisting throughout its life span.
- Datum control & Alignment
Designers need to know that their parts will always come out right even after many trials; they should strive towards ensuring repeatability during setups hence having accurate alignment features like dowel holes, precision locating pins together with datum surfaces among others.
Advantages Of Using CNC Fixtures
Higher Precision
Positioning a component repeatedly thanks to the use cnc fixture leads to accurate machine dimensioning thus better part-making precision being achieved consistently over time.
Enhanced Efficiency
Speeding up setup processes is one thing that these devices do best since they securely clamp down on work-pieces reducing human intervention drastically while at it saving more time for other operations thereby increasing productivity levels within any given manufacturing environment altogether.
Better Quality Control
CNC Fixtures ensure stability throughout the entire manufacturing process thus resulting in superior surface finishes, close tolerances, and less wastage due scrap materials which in turn leads to overall high-quality production levels.
Flexibility
The ability of cnc fixtures to handle different workpiece sizes and shapes is a plus when it comes to versatility since this allows for quick change-over or set up times during mass production runs where components may vary greatly from one batch run unto another thereby reducing operational downtimes significantly.
Cost Effective
Optimizing machine feeds & speeds coupled with accurate positioning will not only cut on production but also lower material costs as there will be less wastage thus increasing profitability.
Conclusion
CNC fixtures are tools used in manufacturing industries for producing the same part repeatedly or assembling many parts together. This guide has provided useful information regarding types and uses of CNC fixtures. If your company requires reliable CNC machining services, kindly contact Easiahome.
