In manufacturing, particularly within the automotive industry, quality assurance and inspection play a pivotal role in product assembly. This is especially true when it comes to precision machining of essential engine components such as crankshafts. Leveraging Computer Numerical Control (CNC) technology for processing these intricate parts requires deep scrutiny at every stage, more so during the quality inspection phase. The task carries numerous challenges and precautions but can improve production rates significantly when meticulously executed.
Considering accuracy as central to this process, an efficient inspection plan must involve parameters related to dimensional accuracy, surface integrity, angularity, straightness, and circularity. Let’s delve into a hypothetical case study involving our shaft being machined on a 5-axis Mazak INTEGREX e-670H multi-function machine, using chisels made from high-speed steel (HSS).
The crankshaft exemplified here features six crankpins with diameters of 57 mm (+/-0.01mm), seven main journals with diameters standing at 60 mm (+/-0.015mm). Additionally, the total length amounts to 700 mm (+/-0.02mm). As the part is crucial to the functionality of an automobile engine, maintaining extremely tight tolerances hold critical importance.
Now let’s unveil the intricacies associated with the quality inspection process for such a workpiece, accounting for over 80% of the article’s premise.
Primarily, due to the complex shape and size of crankshafts, visual inspections become challenging; hence advanced geometric evaluation methods come into play. Since most dimensions cannot be accessed simply by applying calipers or micrometers, we use Coordinate Measuring Machines (CMMs) designed specifically for large components like crankshafts.
Employment of tactile CMM – Hexagon Global S Blue with PC-DMIS CAD++ programming software articulates our instance. However, CMM usage demands expertise due to its comprehensive nature; convoluted part geometry adds another layer of complexity. So, it’s essential that operators are thoroughly briefed on safe and accurate handling of the equipment.
Prior to starting an inspection session, it is necessary to calibrate these instruments according to the parameters defined by ISO 17025. Calibration ensures dependable data engagements along measuring lengths up to 1500 mm for our chosen device with a specified permissible error limit of only (+/-) 1.9 µm.
Another notable challenge relates to maintaining consistent temperature conditions throughout this process, as minor fluctuations can significantly impact measurements and overall final product quality.
Once measurements commence, the machine evaluates the workpiece in six degrees of freedom (6DoF), capturing millions of surface points per rotation. The software then compares the acquired meshed data against CAD designs referring crankpin diameters, circularity, main journal diameters, runout and more. Any deviation triggers alerts ensuring corrective actions happen before erroneous products reach assembly lines.
Surface finish inspections also pose difficulties considering the high dynamic stresses endured by crankshafts while performing. For this, we resort to Mitutoyo Surftest SV-3200, which scrutinizes the Ra and Rz values across lateral surfaces of each pin and journal within +/-5µm boundaries. Maintaining surface smoothness reduces engine wear saving long-term costs for end users.
Quality checks extend further covering hardness testing using Brinell’s method obtaining readings between HB240-HB280 for our HSS shaft. Inspecting magnetic particle becomes necessary when working with ferrous materials spotting minute cracks not visible to naked eyes.
Overall, any stage from first sample tests to last piece control must adhere strictly to qualitative norms manifesting optimal engine performances. Transgressing these precautionary measures compromises customer satisfaction, brand reputability, but above all poses safety threats for product users.
Scrutinizing crankshaft machining through CNC technology is a task demanding high precision. It requires robust inspection equipment, standardized methodologies and vigilant operators to ensure compliance with stringent tolerance limits. The process may be rigorous and exacting, but the rewards that come from delivering quality-assured products in the market far outweigh these challenges.
