Workholding and fixture processes are crucial for the accuracy and efficiency of machine tools. They involve securing the workpiece and the cutting tool in a stable position, while allowing for the desired motion and force. This article will discuss some of the common challenges and solutions for workholding and fixture processes in the context of machine tools.
There are many types of workholding and fixture devices, depending on the shape, size, material, and geometry of the workpiece and the tool. Some of the most common ones are vises, clamps, chucks, mandrels, and arbors. Each type has its own advantages and disadvantages depending on factors like ease of use, flexibility, precision, cost, and durability. Choose the appropriate type based on your machining operation's requirements and specifications.
One of the main challenges of workholding and fixture processes is avoiding errors that can affect the machining operation's quality and performance. Common errors include workpiece deformation, displacement, and damage. Workpiece deformation happens when the workholding or fixture device applies excessive or uneven pressure on the workpiece, resulting in dimensional inaccuracies, surface defects, and tool wear. Workpiece displacement occurs when the workpiece or tool shifts during the machining operation due to vibration, cutting force, or thermal expansion. This can lead to misalignment, chatter, and poor surface finish. Workpiece damage is caused by abrasion, corrosion, or contamination from the workholding or fixture device and can lead to surface flaws, cracks, and reduced strength.
To prevent or minimize errors, optimize your workholding and fixture processes by selecting the appropriate device for your workpiece and applying the correct clamping force and position. Also, make sure you accurately align your workpiece and tool using reference points, indicators, gauges, or sensors. You can reduce vibration and chatter by using rigid and balanced devices, dampening devices, or cutting parameters. Protect your workpiece from damage by using protective coatings, pads, or inserts, and clean your workholding and fixture devices regularly.
To measure and improve workholding and fixture process quality, evaluate them using methods like visual inspection, dimensional inspection, and surface inspection. Visual inspection requires checking the workpiece and tool for any signs of deformation, displacement, or damage. Dimensional inspection involves measuring the workpiece and tool to see if there are any deviations from your desired dimensions. Lastly, surface inspection evaluates the workpiece and tool for any irregularities on the surface. You can use instruments such as calipers, micrometers, verniers, CMMs, profilometers, interferometers, or optical scanners to perform these tasks.
Based on the results of your evaluation, implement corrective actions or preventive measures to improve your workholding and fixture processes. These may include adjusting the device, clamping force, or alignment to reduce errors. You can also replace or repair worn or defective parts, and modify or design parts to enhance their suitability and performance, and implement quality control systems to monitor your processes.
When machining aluminum on steel fixture or table and clamping system you to take in account the difference of thermal growth of the two material. Avoid to constrain the part in its plane parrallel to the clamping surface to prevent part deformation. This apply to any combination of machine, part, and fixture material.
If the machine tool is a highly accurate and high RPM machine, make sure to purchase very high quality toolholders. Low quality toolholders will not only drastically reduce the accuracy of the machine but could actually damage a high RPM spindle.
Bonjour, Je suis d'accord avec vous si vous usinez une pièce en lopin , par contre si c'est du profilé aluminium plusieurs contraintes rentrent en compte ( serrage, parallélisme et longueur à usiner ..etc )et se rajoute une tolérance serrée ??