QUALITY CONTROL in Tool Design Engineering

QUALITY CONTROL in Tool Design Engineering

Quality control is the entire collection of activities through which we achieve fitness for use.
It is a system of routine technical activities, to measure and control the quality of the inventory as it is being developed.

Objectives of quality control:

• Evaluation of quality standard's of incoming material, product in actual manufacturing and of outcome product.
• Judging the conformity of the process to the established standards and taking suitable action when deviations are noted.
• Evaluation of the optimum quality obtainable under the given condition
• To improve quality and productivity by the pre-control and experimentation.
• Identify and address errors and omissions.
• Provide routine and consistent checks to ensure data integrity, correctness, and completeness.

Quality assurance:

Quality Assurance covers all activities from design, development, production, installation, servicing and documentation. This introduced the rules: "fit for purpose" and "do it right the first time". It includes the regulation of the quality of raw materials, assemblies, products and components; services related to production; and management, production, and inspection processes.

One of the most widely used paradigms for QA management is the PDCA (Plan-Do-Check-Act) approach, also known as the Shewhart cycle.

Failure testing

A valuable process to perform on a whole consumer product is failure testing, the operation of a product until it fails, often under stresses such as increasing vibration, temperature and humidity. This exposes many unanticipated weaknesses in a product, and the data is used to drive engineering and manufacturing process improvements. Often quite simple changes can dramatically improve product service, such as changing to mould-resistant paint or adding lock-washer placement to the training for new assembly personnel.

Statistical control

Many organizations use statistical process control to bring the organization to Six Sigma levels of quality, in other words, so that the likelihood of an unexpected failure is confined to six standard deviations on the normal distribution. This probability is less than four one-millionths. Items controlled often include clerical tasks such as order-entry as well as conventional manufacturing tasks.

Traditional statistical process controls in manufacturing operations usually proceed by randomly sampling and testing a fraction of the output. Variances of critical tolerances are continuously tracked, and manufacturing processes are corrected before bad parts can be produced.

Company quality

During the 1980s, the concept of “company quality” with the focus on management and people came to the fore. It was realized that, if all departments approached quality with an open mind, success was possible if the management led the quality improvement process.
The company-wide quality approach places an emphasis on three aspects:-

1. Elements such as controls, job management, adequate processes, performance and integrity criteria and identification of records
2. Competence such as knowledge, skills, experience, qualifications
Soft elements, such as personnel integrity, confidence, organizational culture, motivation, team spirit and quality relationships.
The quality of the outputs is at risk if any of these three aspects are deficient in any way.
The approach to quality management given here is therefore not limited to the manufacturing theatre only but can be applied to any business activity:

• Design work
• Administrative services
• Consulting
• Banking
• Insurance
• Computer software
• Retailing
• Transportation

It comprises a quality improvement process, which is generic in the sense it can be applied to any of these activities and it establishes a behavior pattern, which supports the achievement of quality.

This in turn is supported by quality management practices which can include a number of business systems and which are usually specific to the activities of the business unit concerned.
In manufacturing and construction activities, these business practices can be equated to the models for quality assurance defined by the International Standards contained in the ISO 9000 series and the specified Specifications for quality systems.

Still, in the system of Company Quality, the work being carried out was shop floor inspection which did not control the major quality problems. This led to quality assurance or total quality control, which has come into being recently.

Total quality control:

Total Quality Control is the most necessary inspection control of all in cases where, despite statistical quality control techniques or quality improvements implemented, sales decrease.
The major problem which leads to a decrease in sales was that the specifications did not include the most important factor, “What the customer required”.
The major characteristics, ignored during the search to improve manufacture and overall business performance were:

• Reliability
• Maintainability
• Safety

As the most important factor had been ignored, a few refinements had to be introduced:

1. Marketing had to carry out their work properly and define the customer’s specifications.
2. Specifications had to be defined to conform to these requirements.
3. Conformance to specifications i.e. drawings, standards and other relevant documents, were introduced during manufacturing, planning and control.
4. Management had to confirm all operators are equal to the work imposed on them and holidays, celebrations and disputes did not affect any of the quality levels.
5. Inspections and tests were carried out, and all components and materials, bought in or otherwise, conformed to the specifications, and the measuring equipment was accurate, this is the responsibility of the QA/QC department.
6. Any complaints received from the customers were satisfactorily dealt with in a timely manner.
7. Feedback from the user/customer is used to review designs.
8. Consistent data recording and assessment and documentation integrity.
9. Product and/or process change management and notification.

PRACTICAL CONSIDERATIONS IN DEVELOPING QA/QC SYSTEMS:

Implementing QA/QC procedures requires resources, expertise and time. In developing any QA/QC system, it is expected that judgments will need to be made on the following:
Resources allocated to QC for different source categories and the compilation process;
Time allocated to conduct the checks and reviews of emissions estimates;
o Availability and access to information on activity data and emission factors, including data quality.
o Procedures to ensure confidentiality of inventory and source category information, when required.
o Requirements for archiving information.
o Frequency of QA/QC checks on different parts of the inventory.
o The level of QC appropriate for each source category.
o Whether increased effort on QC will result in improved emissions estimates and reduced uncertainties.
o Whether sufficient expertise is available to conduct the checks and reviews.

INSPECTION:

Inspection may be defined as the measurement of the dimensions / form / profile of the component as specified by the designer. The above described form of inspection is termed as Measurement, aided by instruments.

PURPOSE OF INSPECTION:

o By thorough inspection, we can detect faults at every manufacturing process and rectify them.
o To remove defective or incorrectly made parts as soon as fault occurs.
o It helps in building up the reputation of a firm or concern.
o It improves quality of the product.
o It reduces cost spent on scrap pieces and further process can be stopped if mistake is going on.
All parts are inspected in their respective stages while processing. This knows as stage inspection. It helps in rectifying the mistake occurred during each operation. Final inspection is one in which the product manufactured is inspected completely after completion of all final assembly.

INSPECTION CHECK LIST:

1) Check for the dimensional accuracy of the finished product.
2) Check for the surface finish of the finished product.
3) Check for damage, scratch and deformation accrued in the product.
4) Check for proper fractioning of the mould.
5) Check for proper assembly of the mould
6) Check for leakage in the cooling circuit.

MEASURING RANGE:

Range may be defined as the values (Min-Max value) for which the instrument can be used for measurement.

ACCURACY:

The closeness of the measured value with the true value of the measured quantity is termed as Accuracy.

PRECISION:

Precision may be defined as the responsibility of the measuring process; repeatability may be defined as the capability of the measuring process to indicate the same value for a measured quantity under different trials.

The different methods of measurement are listed below:

Direct Method of Measurement: The value of a quantity is obtained directly by comparing the unknown with a standard. Ex: scale, weighing instrument, vernier, and micrometer.
Indirect Method of Measurement: Several parameters of the measured directly and then the value is obtained by performing mathematical calculations. Ex: Density measurement by weighing the mass and measuring the geometrical dimensions.

Comparison Method of Measurement: Comparison of the measured quantity with known value of the same quantity with known value of the same quantity or another quantity. Ex: GO and NOGO gauges indicate whether the values are within the permissible range or not.
Some of the terms in the measurement process are explained below:

Basic Size: It can be defined as the size of a part in relation to which all limits of variation are determined.

Limits: These are the two extreme permissible sizes foe any dimension.

Tolerance: It is the difference between the high and low limits of size. It isnecessary to specify this because of the inaccuracies in the manufacturing process and reasonable inaccuracy in the workmanship. It can be Unilateral or Bilateral.

Allowance: An intentional difference between hole dimension and shaft dimension for any type of fit (clearance, Interference, Transition fit). Maximum allowance is obtained by subtracting the Min. shaft size with the largest hole size and Min. allowance is obtained by subtracting the largest shaft and the smallest hole size. The allowance is positive for clearance fit and negative for interference fit.

Deviation: Algebraic difference between actual and the basic size. Upper deviation is defined as the max. Limit of size and the corresponding basic size. Lower deviation is defined as the minimum limit of size and the corresponding basic size.

The following measuring instruments found at Inspection department:

Micrometer, Calipers, height gauge, Slip gauges, gauges, filler gauge, and magnifying lens, etc.
Precision Tools and Gages:

• Micrometers, Slide Calipers, Calipers, Dividers.
• Tool Sets, Squares, Protractors, Angle Measurements, Precision Rules, Straight Edges, Parallels.
• Electronic Data Collection Systems, Gage Amplifiers, Hardness & Surface Testers.
• Dial & Electronic Indicators & Gages, Height Gages, Depth Gages.
• Thread Gaging, Hole Gages, Slot Gages, Fixed Gage Standards.