Industry News
How To Overcome Common Quality Issues When Machining Composite Materials?
2026-06-23
Over the course of more than two decades in which FRIMA has served clients across the global automotive, aerospace and medical device sectors, we have found that quality control in the machining of composite materials remains a widespread challenge within the industry. Unlike homogeneous metallic materials, the anisotropy and high abrasiveness of composite materials such as carbon fibre, glass fibre and aramid can easily lead to issues such as edge delamination, fibre pull-out, surface burrs and rapid tool wear. These seemingly minor defects often result in parts being scrapped, a sharp rise in re-machining costs and delays to delivery schedules, ultimately eroding project profits.
Many engineers tend to attribute quality issues solely to tool performance, however, based on our practical experience, high-quality machining results are the outcome of the synergy between tool selection, clamping solutions and process parameters. Drawing on real-world data and case studies from FRIMA’s front-line production, this article systematically analyses common quality pain points in composite machining and provides optimisation solutions that can be implemented immediately.
The Three Key Quality Challenges in Composite Materials Machining and Their Underlying Causes
Before discussing solutions, we must first identify the root causes of the problems: the performance advantages of composite materials stem from their composite structure of fibres and resin matrix; however, it is precisely this structure that presents specific challenges not encountered in metal machining.
1. Edge delamination and fibre pull-out
When the cutting angle is inappropriate, the cutting tool will pull on the fibres rather than cutting them cleanly, leading to separation between material layers and the lifting of fibre ends. This is the most critical defect in composite materials; it not only affects appearance but also directly weakens the structural strength of the component.
2. Poor surface finish and burrs
As the cutting edge of the tool becomes dull due to wear, combined with workpiece vibration during machining, this results in residual fibres on the surface and surface roughness that fails to meet specifications. The vast majority of factories are required to arrange an additional manual grinding process, which incurs high labour costs and results in extremely poor part consistency.
3. Excessively rapid tool wear and significant quality fluctuations
Carbon fibre is dozens of times more abrasive than ordinary steel, causing the cutting edges of standard carbide tools to dull rapidly. This not only drives up tool procurement costs but also leads to a continuous decline in machining quality within the same batch of parts as the tools wear down, resulting in extremely unstable yield rates.
Diamond-Coated End Mills: The Key Solution to Abrasive Milling Challenges
Why are Standard Carbide Tools Unsuitable for Machining Composite Materials?
Carbon fibre and glass fibre have a hardness close to that of corundum, the cutting process is effectively equivalent to countless microscopic abrasive particles continuously grinding away at the tool’s cutting edge. In FRIMA' s tests, standard fine-grain carbide end mills used to machine continuous carbon fibre panels often exhibited significant edge wear after just 8–12 parts; this is followed by quality issues such as delamination and burrs, whilst frequent tool changes also significantly reduce machine utilisation rates.
Performance Advantages of Diamond-Coated Tools and FRIMA' s Empirical Data
CVD diamond-coated tools involve depositing a micrometre-thick diamond film onto the surface of a cemented carbide substrate, combining the toughness of the substrate with the ultra-high hardness of diamond. They currently represent the most cost-effective solution for composite material milling applications.
In FRIMA’s comparative mass-production tests, under identical operating conditions, the service life of diamond-coated end mills was 8 to 12 times that of standard carbide tools, yielding highly significant quality benefits:
● The cutting edges remain sharp for extended periods, resulting in cleaner cut surfaces and reducing the defect rate for delamination and fibre pull-out by over 85%
● Surface finish consistency across parts in the same batch reaches 98% , eliminating quality fluctuations such as ‘the first few parts passing inspection whilst the last few are scrapped’
● Tool changes and downtime are reduced by over 80% , with overall machining efficiency improving by more than 40%
We previously machined carbon fibre battery box structural components for a new energy vehicle client. Initially, we used imported carbide cutting tools, which required tool changes every 8 parts produced, with a delamination rate at the part edges as high as 22% ; this necessitated the deployment of three workers dedicated to grinding burrs. After switching to customised diamond-coated end mills and optimising the cutting parameters, a single tool could machine 95 parts consecutively, the delamination defect rate fell to 1.5%, the manual grinding process was completely eliminated, and the overall cost per part was reduced by 37%.
Workholding System Optimization: A Foundational Element of Quality Often Overlooked
Many clients overlook the impact of workholding on the machining quality of composite materials. However, FRIMA’s quality traceability data reveals that nearly 40% of issues involving delamination and chatter marks stem from inadequate workholding strategies.
The fundamental difference between composite materials and metals lies in their properties: composites possess low interlaminar shear strength, making them susceptible to crushing and delamination under excessive localized pressure. Furthermore, thin-walled composite parts lack rigidity and are prone to chatter during machining, which leads to surface chatter marks and edge chipping. Often, problems persist even when using premium cutting tools because the workholding setup fails to meet the necessary standards.
FRIMA' s Common Workholding Optimization Solutions for Composites
1. Full-Surface Vacuum Clamping
For flat composite parts, we replace traditional mechanical clamps with vacuum suction systems. This distributes clamping force evenly across the entire back of the workpiece, preventing localized crushing while effectively suppressing machining vibrations—an efficient method for enhancing surface quality.
2. Customized Flexible Fixtures
For parts with complex, curved geometries, we machine flexible clamping jaws and support fixtures based on the workpiece's digital model. This ensures a perfect fit against the part's surface profile, preventing deformation in unsupported areas caused by cutting forces.
3. Adjustable Auxiliary Supports
For thin-walled or deep-cavity parts, we add auxiliary supports in vibration-prone zones. This significantly boosts the rigidity of the machining system, mitigating chatter at its source.
Our project statistics show that optimizing the workholding strategy alone can help clients reduce chatter marks and clamping-induced delamination defects by more than 60%.
PCD Inserts: A Performance Leap in Composite Material Turning
When turning composite components such as tubes and shafts, cutting tools face more severe abrasive challenges than in milling operations. Because the cutting edge remains in constant contact with the material, standard carbide inserts wear out rapidly, making it difficult to ensure consistent surface quality.
Technical Characteristics of PCD Inserts
Polycrystalline Diamond (PCD) inserts feature a cutting edge formed by sintering diamond particles onto a carbide substrate under high temperature and pressure. The diamond layer is significantly thicker than the coatings found on coated tools, offering superior wear resistance—making them ideal for continuous turning operations.
Real-World Results with FRIMA Turning Processes
We undertook a precision turning project for long carbon fiber tubes. Initially, we used fine-grained carbide inserts; however, the inserts required replacement after machining just three parts, and the surface roughness only reached Ra 3.2, with visible burrs along the edges. After switching to PCD inserts:
● A single insert could machine over 120 parts continuously—a 40-fold increase in tool life.
● Surface roughness consistently stayed within Ra 0.8, eliminating the need for subsequent polishing.
● Cut edges were clean and free of delamination, completely removing the need for secondary trimming.
For high-volume production of composite turned parts, PCD inserts may have a higher initial purchase price; however, when considering the total lifecycle costs—including tooling, labor, and yield improvements—the overall cost can be reduced by more than 50%, making them a highly cost-effective choice.
Optimizing Often-Overlooked Process Details
Beyond tooling and workholding, FRIMA further enhances composite machining quality by optimizing specific process details—insights we also share with clients during DFM consultations.
1. Toolpath Optimization
We prioritize climb milling strategies and carefully plan tool entry methods to minimize fiber pull-out. During 5-axis machining, we maintain an optimal cutting angle relative to fiber orientation, thereby fundamentally reducing the risk of delamination.
2. Matching Cutting Parameters
We customize spindle speeds and feed rates based on the specific fiber content and resin system of the material. This prevents resin matrix softening caused by excessive cutting heat, as well as fiber pull-out resulting from excessively low feed rates.
3. Selection of Cooling Methods
Water-based coolants are generally avoided in composite machining. Instead, we typically employ air cooling or Minimum Quantity Lubrication (MQL); these methods effectively dissipate cutting heat while preventing moisture absorption by the resin, which could otherwise compromise material performance.
Inquire Now: Get Your Customized Process Optimization Plan
If you are facing quality challenges in composite material processing or wish to optimize your current manufacturing methods, FRIMA’s technical team offers complimentary drawing reviews and process optimization recommendations. Simply send your part drawings and technical specifications to info@frimaparts.com or complete the online inquiry form on our website; our process engineers will contact you within 24 hours to provide a tailored solution.
FAQ
Q1: What is the difference between diamond-coated cutting tools and PCD inserts, and how should one choose between them?
A: Diamond-coated cutting tools involve depositing a thin layer of diamond onto the surface of a carbide tool; they are relatively low-cost and suitable for intermittent cutting applications such as milling. PCD inserts have a thicker diamond layer and offer greater wear resistance, making them suitable for continuous cutting applications such as turning, as well as high-volume machining with high-precision requirements. FRIMA will recommend the most cost-effective tooling solution based on your part type, machining process and production volume.
Q2: Can all composite materials be machined using diamond-coated tools?
A: Yes, diamond-coated tools are suitable for the vast majority of composite materials, including carbon fibre (CFRP), glass fibre (GFRP), aramid fibre and honeycomb sandwich structures. They can effectively improve machining quality and extend tool life.
Q3: Is tooling always to blame for delamination during composite machining?
A: Not necessarily. The causes of delamination are highly complex; tool wear, clamping deformation, inappropriate cutting parameters and incorrect toolpaths can all lead to delamination. FRIMA’s engineers will systematically investigate the issue to identify the root cause and provide a comprehensive solution, rather than simply recommending a tool replacement.
Q4: Thin-walled composite parts are prone to warping during machining. What solutions are available?
A: Controlling warpage in thin-walled composite parts requires multi-dimensional optimisation: utilising uniform clamping methods such as vacuum suction cups; selecting sharp diamond tools to reduce cutting forces; optimising toolpaths to minimise cutting stresses; and adopting a high-speed, low-feed cutting strategy. We possess extensive experience in machining thin-walled parts and can tailor a bespoke process solution based on the specific characteristics of your part.