Quality Control Checklist for a Mechanical Device

Engaging contractors for product development can significantly speed up the process, but it demands careful planning and rigorous quality control. To ensure that the final product meets technical requirements—and to avoid misunderstandings and delays—all project details should be clearly agreed upon in advance with the contractor, including technical specifications, timelines, and acceptance criteria. In this checklist for quality assurance, we will discuss the essential aspects of quality control that will help you assess whether the final mechanical product or prototype aligns with technical requirements and prevent any disappointment with the results achieved.

Product Lifecycle Stages and Quality Control Checklist

3D Model Development QA

The 3D model is the foundation for successful design and manufacturing. The quality and completeness of the model directly impact the functionality and reliability of the final product. The questions below will help you assess the quality of your 3D model.

• Do the dimensions of the 3D model meet the specifications outlined in the technical requirements?
• Does the accuracy of the 3D model align with the technical requirements?
• Does the level of detail in the model meet the requirements for subsequent design stages?

For simulations, the geometric form of the 3D model is often simplified, whereas a model prepared for 3D printing should fully replicate the geometry of your product.

• Does the model match the original design documentation in terms of component composition?
• Are there clearly defined locations in the model for all electronic components?
• Do the dimensions and shapes of mounting points align with the component dimensions?
• Are adequate clearances and distances between components maintained to prevent overheating and short circuits?
• Have shielding and electromagnetic compatibility requirements been taken into account?
• Are all connections between elements (mechanical, electrical, hydraulic, etc.) accurately represented?
• Are all fastening elements (bolts, nuts, washers, etc.) present in the model and correctly positioned?
• Have all necessary sealing elements (gaskets, rings, etc.) been included?
• Has the 3D model been checked for errors, such as gaps, overlapping surfaces, or misaligned parts?
• Are wear factors such as friction and corrosion considered in the model?
• Is the model adapted for the selected production method (e.g., 3D printing, injection molding)?
• Does the model take into account the manufacturing constraints of your production facility?
• Is the model built using the correct coordinate system?

Incorrect coordinate system usage: If a left-handed coordinate system is used for modeling a part and a right-handed system for assembly, it can lead to assembly errors.
Insufficient positioning precision: If hole coordinates in a part lack sufficient precision, this can cause assembly issues and functional failures in the product.

• Are all elements of the model built within the same coordinate system?
• Is the model saved in a compatible format that can be opened in required CAD systems?
• Are there no errors upon importing/exporting the model?

Parts and Assemblies Production Quality Control

The quality of a manufactured part is determined by a set of characteristics. We recommend checking key parameters, such as geometric accuracy and surface quality. Below is a list of essential acceptance criteria for manufactured products:

• Do all linear dimensions, diameters, angles, and other geometric parameters of the part conform to the drawings and technical specifications?
• Are the actual tolerances and fits consistent with those specified in the drawings and standards?
• Are there deviations from nominal tolerance values that could impact part functionality?
• Does the actual surface roughness meet the cleanliness class specified in the drawings?
• Are there any visible defects on the part’s surface, such as burrs, cavities, cracks, pores, inclusions, etc.?
• Is the part’s surface free from mechanical damage (scratches, cracks, chips)?
• Are all sharp edges and corners rounded according to safety and manufacturability requirements?
• Are there no protruding elements that could damage other parts or cause injuries?
• Does the quantity of manufactured parts match the quantity specified in the technical documentation?

Assembly Quality Control

Assembly is the final stage of production, requiring high precision and adherence to sequence. The quality of the assembly directly impacts the functionality and reliability of the finished product. Below are key questions to help assess assembly quality:

• Are all parts of the device assembled in the correct sequence according to the assembly diagram?
• Are there no loose connections that could lead to leaks, vibrations, or other issues?
• Are welded, soldered, and bonded joints executed correctly?
• Do actual gaps and clearances meet the allowable values specified in the technical documentation?
• Are there no misalignments that could affect the device’s functionality?
• Is the required structural rigidity and strength achieved?
• Are surface cleanliness requirements met after welding, soldering, or bonding?
• Are all parts and components listed in the specifications present in the assembly?
• Do part types and markings match those specified in the documentation?
• Is the protective coating on all parts intact?
• Are there no scratches, chips, or other damage to the coating?
• Are the coating quality requirements outlined in the technical documentation met?

Testing QA

The testing process involves a series of trials to confirm that the finished product or prototype meets the specified requirements and can perform its functions under required conditions. We have compiled a list of key questions to assess the quality of a developed prototype or finished product:

• Does the device perform its stated functions?
• Do the product’s mechanisms operate smoothly and accurately?
• Can the device withstand the specified loads and environmental stresses?
• Is the device capable of functioning in the required conditions without failures or breakdowns?
• Are the device's connections leak-proof?
• Are the noise, vibration, and other parameters within acceptable limits?
• Is the necessary range of motion provided for each part?

‍Insufficient mobility: If moving parts of the mechanism are too tight, this can lead to overheating and premature failure.
‍Excessive mobility: If there is too much clearance between moving parts, it can reduce the mechanism's operational accuracy and increase vibration levels.

• Are there no instances of binding, sticking, or other issues affecting part mobility?

Quality Management Systems

Before starting the development of a new device, it’s crucial to understand where and how it will be used. This allows for consideration of all specific requirements, including regulatory standards, industry guidelines, and customer expectations.

• ISO 9001: An international standard that sets requirements for a quality management system.
• Other Standards: Depending on the industry and product specifics, additional standards may apply.

Food Industry:

• ISO 14159: An international standard specifying general safety requirements for machinery used in the food industry.‍
• FDA 21 CFR Part 1: A U.S. standard detailing general requirements for food products, including equipment used in their production and packaging.

Medical Industry:

• ISO 13485: An international standard for quality management systems in medical devices.‍
• 21 CFR Part 820: A U.S. standard establishing quality system requirements for the manufacture of medical devices.

Consumer Goods:

• ‍IEC 60335: A series of standards that specify safety requirements for household and similar electrical appliances.

Quality Assessment Criteria

Quality assessment criteria encompass a wide range of characteristics, from functionality to aesthetics. When developing a new device, numerous factors must be considered to ensure its competitiveness and user safety. To effectively oversee a contractor based on the provided checklist, it is essential to adhere to standards and answer a series of questions.

Functionality:

• What specific tasks is my product intended to accomplish? Are all stated functions fully implemented?
• How reliably does the device perform its core functions? What potential failures could occur, and how might they affect user experience?
• Is it possible to expand functionality by adding new modules?

Reliability:

• What is the projected lifespan of the product as a whole and its key components?
• Which factors are most likely to impact the device’s lifespan (e.g., usage intensity, operating conditions)?
• Is the product resistant to external influences (temperature, humidity, vibration)?
• How often will consumables need replacing or software updates be required?
• How does the product behave under prolonged use? Are overheating, lagging, or other issues likely?

Safety:

• How safe is the product for the user? What safety measures are built into the design and software?
• Does the product comply with industry safety standards?
• What potential risks could arise during use, and how are they minimized?

Ergonomics:

• How convenient is the product to use? Is the interface intuitive?
• Is it easy to learn all the product’s functions?
• Is physical strain on the user minimized?

Aesthetics:

• Is the appearance appealing to the target audience?
• Do the materials and finish quality align with the premium or mass-market segment?
• Does the product’s design reflect its intended positioning?

It is important to recognize that quality assessment criteria may vary depending on the specific device and its intended use. For instance, in medical equipment, safety and ergonomics are paramount, while for industrial equipment, reliability and functionality take precedence. Our article on the 5 BABOK Approaches explores prioritizing product requirements during development.

Quality Control Methods

Quality control methods are a set of tools and procedures that enable the determination of whether a product meets specified requirements. The choice of specific methods depends on the type of device, the production stage, and the required precision of assessment.

• Visual Inspection: Assessment of the device’s appearance for cracks, scratches, contamination, and other defects.
• Dimensional Inspection: Verification of device dimensions, checking angles, alignment, surface quality, and more.
• Functional Testing: Evaluation of device performance under various operating modes and conditions, including durability testing.‍
• Physical Testing: Determination of mechanical characteristics of materials (tensile, compressive, and bending strength), hardness, and impact toughness assessment.

In closing,

For anyone developing a mechanical device with a contractor, quality control is a non-negotiable part of the process. It’s vital to stay involved at every stage, from the initial 3D model to the final testing. Make sure to communicate clear technical requirements and keep the lines of communication open to avoid misunderstandings.

Implementing straightforward quality checks—like visual inspections, measurements, and functional tests—can help catch issues early. This not only saves time and reduces costs but also ensures that the final product meets your expectations and those of your customers.