Exceeding Tolerances: Causes and Control strategies
Precision mechanical processing is a technical process that demands high accuracy and finesse in every detail of the product. During this machining process, tolerance plays a crucial role in ensuring that the final product meets quality and precision requirements. However, exceeding allowable tolerances can lead to serious consequences for the product and overall production process.
What are tolerances?
Tolerances refer to the permissible gap between two limits of a part or between a part and surfaces affected by external factors. In precision mechanical processing, these tolerances are carefully designed to ensure that the parts can function accurately when assembled and used under real operating conditions.
Types of common tolerances
Dimensional tolerances
These specify the allowable deviation in dimensions of a part or between parts when assembled. For example, dimensional tolerances may govern the permissible difference between the outer diameter and inner diameter of a tube, or the length of a shaft.
Form tolerances
These define variations in the shape of a part, such as the straightness of an edge, the curvature of a surface, or the tilt of a plane relative to a reference surface.
Position tolerances
Used to specify the alignment between features or the location of parts. Position tolerances measure distances between holes, the inclination of surfaces, or deviations between reference points.
Surface tolerances
Define the surface quality of parts, including characteristics like smoothness, paint thickness, or surface gloss.
Orientation tolerances
Used to specify the orientation of a part, such as the inclination of a shaft relative to a reference plane.
Risks of exceeding tolerances
Assembly fit and alignment
Excessive tolerances can reduce the ability to fit and align parts properly. This can result in parts not fitting correctly or requiring excessive force to assemble, thereby reducing aesthetic appeal and the accuracy of the final product.
Accuracy and stability
Large tolerances can significantly affect the accuracy of parts and the stability of the product. Parts may not achieve desired precision, especially in applications requiring high accuracy, such as in medical, aerospace, or electronic fields.
Product performance and durability
Uncontrolled tolerances can impact the performance and durability of the product. In harsh conditions, excessive tolerances may cause uneven wear, accelerate deterioration, and reduce product lifespan.
Manufacturing costs and recycling
Exceeding tolerances can lead to increased production costs due to the need for modifications or rework of parts. Additionally, recycling products or materials can become more challenging if tolerances are not closely controlled from the outset.
Quality and brand reputation
Excessive tolerances can diminish product quality and affect the company’s brand reputation. A product that fails to meet expected precision and durability may lead to customer dissatisfaction and loss of market share.
Safety and regulatory compliance
In some cases, exceeding tolerances can lead to safety issues and non-compliance with industry regulations. This is particularly critical in high-safety applications such as medical or aerospace fields.
Control strategies for tolerances
To control tolerances in precision mechanical processing and ensure that products meet desired quality and accuracy
Precise engineering design
Design products with appropriate tolerances. Engineers should have deep knowledge of tolerance stack-ups and apply international standards such as ISO, ANSI to establish reasonable tolerance limits.
Selection of appropriate machining processes
Carefully choose machining processes like CNC turning, CNC milling, grinding, drilling, etc., to meet tolerance requirements effectively and ensure product accuracy and durability.
Production process control
Strictly control the manufacturing process, including setting up quality inspection procedures and rigorously inspecting machining operations. Use measuring devices to ensure product accuracy.
Use of modern technology
Employ modern machining and quality inspection technologies to maintain tolerances within permissible limits.
Employee training
Train staff in measurement techniques, use of technologies, and quality control processes to ensure product accuracy.
In precision mechanical processing, tolerances play a crucial role in ensuring the accuracy and performance of the final product. Controlling tolerances is key to meeting quality standards, technical requirements, optimizing production processes, and minimizing unnecessary costs.
