Quality assurance in the production of mountain bikes

Control of raw materials

Quality control begins with the inspection of the raw materials used and their manual or mechanical processing. This is the only way to produce frame components that meet all the specifications from the design and withstand the calculated loads. In addition, conscientious quality control in series production ensures that the properties of all frame components remain the same.
The properties of frame parts made of CFRP material depend heavily on careful manufacturing. After a component has been completed, possible production defects such as defective material or unclean alignment of the carbon layers can only be detected with extremely high effort. In the course of quality control, efforts are therefore made to eliminate material defects and defective parts from the manufacturing process as early as possible.

Quality assurance in frame building

The series production of all ROTWILD carbon frames takes place in one of the most modern factories in Asia. For quality assurance during the construction of the frame, a Standard Operating Procedure (SOP) is defined for each individual process step. This covers the inspection of all workpieces, auxiliary materials, operating materials and work instructions. The individual quality checks can be divided into four steps:

1. Incoming goods inspection of raw materials, prefabricated raw materials and individual and add-on parts.
2. Quality controls between the individual departments: Raw parts processing, CNC machining, surface finishing, painting.. 
3. X-ray fluoroscopyt. 
4. Mechanical testing - load tests. 
5. Final inspection per test report.

1. incoming goods inspection

Flawless materials are the prerequisite for high quality of the finished product. This step therefore involves checking whether the various starting materials are free of defects and can therefore be used in production without hesitation. The following are checked: carbon prepregs, glass fiber mats, resins, PU moldings, polystyrene cores, metal inserts (threaded inserts, blanks for subsequent CNC machining), bearings (rear triangle, headset, etc.), screw fittings (standard and special parts), inlays (dropouts, covers, other inserts), frame parts (linkage), frame protectors, decorative and protective foils.

2. quality controls and in-process quality assurance between the individual departments

Cutting

High-quality components require flawless starting material. For this reason, the individual carbon blanks are first visually inspected for defects, fiber distortion or fabric damage. Then, for documentation purposes, all blanks are assigned to the correspondingly numbered material batch. Finally, the machine-produced blanks are compared with the specifications and the material batch is assigned to the specific component.

Clutch

For error-free production, the individual laminating steps are described in a lay-up plan, both pictorially and in writing. For documentation purposes, each frame is given a unique QR code.

Hardeningn

For this work step, quality assurance defines clear curing parameters. These apply to the contact pressure on the mold halves and molds, the pressurization of air bubbles inside, the temperature profile and the curing time.

Quality control after demolding (blank)

This step ensures that there is no confusion in the molds used for the frame parts and the tools. A visual inspection of the frame blank is carried out with a particular focus on: Resin accumulation (lack of fibers), wrinkles in the scrim, delamination, contamination (particles), dents, holes, fractures, damage due to demolding, condition of the inserts (no deformation), shape of the cavities (defective internal printing - air bladder), condition of the tools (mold halves, sliders). In order to detect the smallest production defects, printing is performed in a water bath. Here, the air-filled frame blank is immersed. Rising air bubbles reveal poorly processed areas.

CNC machining

Various frame parts are machined in production with CNC milling machines. An exact description of the machining steps per part, the listing of the CAM programs to be used and the definition of the milling cutters and coolants guarantee high product quality. After each machining step, the machined surfaces are randomly checked using measuring tools and test gauges, thus validating the process parameters.

Bonding 

The components to be used for bonding the frame parts are precisely defined. The same applies to the cleaning agents, adhesives, etc. used. Precise documentation of the individual work steps makes it possible to check whether all processing specifications have been adhered to. The gauges used for positioning the frame parts during bonding are also recorded in the documentation for this work step.

Quality control after mechanical processing 

In this step, all dimensions and interfaces of the frame blank are checked. First, all frame dimensions are checked on the basis of the dimensioned drawing. The position of the bearings and the mounts for the motor and battery are also checked against the specifications on the dimensional drawing. 

Then the frame interfaces are checked. Here, the clearance of the tires, the rear triangle, the crank and the chainrings are checked. Also the cable bushings, the alignment or distortion of the frame (axles, straightness) and all connection dimensions on the bottle cage, the seat tube diameter, the axle width and the brake mount are checked. 

Fullnessn & slurry 

After all dimensions of the frame blank have been adjusted, the surface is ground. During this process, the surface finish is continuously visually inspected. The frame does not meet the requirements until all burrs have been removed, all surfaces smoothed, and all uncleanly processed laminate layers filled in. 

Quality control - handover to the painting department 

Before the frame blank is painted, a visual inspection is carried out with a special focus on color changes and fabric defects in the visible carbon, cleanly smoothed surfaces, possible holes due to missing material, scratches, dents, droplets and bubbles. Also checked is whether all body edges are visible as intended by the design and have not been smoothed by excessive sanding. In addition, the blank is checked for possible contamination by particles in the laminate and the hardness of the surface is checked.

Painting

For quality assurance purposes, the cleaning agents, primer, colors and masking films used in the painting process are precisely defined. The same applies to the colors, the artwork (masking) and the finish (matte, glossy). After each intermediate step, a visual check of the masking, the color tones and the surface quality is carried out.

Decor

After painting, the decor is applied. For all the stickers to be used, there are precise specifications in terms of their size, position, colors and material. During the application, the applied number, type and position are visually checked.

Quality control after painting and decor

Once all the decors have been applied, a final visual inspection of the frame is carried out. The aim here is to rule out paint damage, masking defects, discoloration, undesirable matte and gloss effects, orange peel, droplets and bubbles, scratches, dents and incorrect positioning and incompleteness of artwork and decor. The properties of the surfaces in terms of their layer thicknesses, impurities (particle density), hardness and resistance (drop-ball test) are also checked.

Mounting

3. fluoroscopy by X-ray machine