High-voltage connectors and signal connectors used in new energy vehicles, energy storage, and photovoltaic equipment operate in complex temperature environments for extended periods. Outdoor energy storage cabinets, new energy vehicle engine compartments, and interiors of distributed photovoltaic inverters experience temperatures as low as -40 degrees Celsius in winter and as high as 85 degrees Celsius after exposure to direct sunlight in summer. Daily start-ups and shutdowns, along with seasonal changes, result in dozens of cycles of hot and cold temperatures. Many connector manufacturers face same challenge: samples pass all tests at room temperature, but after high and low temperature cyclic aging tests, defects such as fluctuations in mating force, air leakage, pin coaxial misalignment, and insufficient insulation gaps occur, causing products to fail to meet automotive and energy storage equipment standards.

 

After disassembling and tracing source of numerous aging failure samples, it was found that root cause of most connector thermal failures was not plastic raw materials or metal pins, but rather fluctuations in dimensions of connector mold cavity. Core molding structures of connectors, such as shell, core, sealing groove, and pin positioning groove, are susceptible to damage if cavity dimensional deviation exceeds 0.005mm. After dozens of cycles of high and low temperature contraction and expansion, internal stress of plastic parts is continuously released, causing slight deformation, ultimately compromising connector's sealing and conductive mating structure.
Many mold processing plants only perform dimensional inspection at room temperature, ignoring differences in plastic deformation caused by cavity structure under hot and cold conditions. They loosen dimensional tolerances to 0.01mm or even larger during cavity processing. Short-term tests of delivered samples may not reveal problems, but batch failures occur during aging tests. This article, based on a real-world case study of connector aging tests, systematically dissects supporting logic of 0.005mm cavity structure for high and low temperature stability, and outlines the entire control process from mold design, processing, heat treatment to aging test verification. It provides connector manufacturers with implementable mold verification standards, addressing problem of thermal cycling failure at source.

Glass fiber modified plastic materials used in connectors, such as PA66, PPS, and LCP, exhibit significant thermal expansion and contraction characteristics, with a fixed difference in the amount of shrinkage and expansion across different temperature ranges. Mold cavity is reference carrier for molding plastic parts; every aspect of cavity—wall thickness, groove depth, positioning coaxiality, and sealing surface dimensions—is directly replicated onto finished connector. Cavity deviations exceeding 0.005mm will continuously amplify deformation defects during thermal cycling, leading to four typical aging failure problems.
1. Sealing Groove Cavity Deviation, Waterproofing and Airtightness Failure After High and Low Temperatures. Annular sealing groove on connector shell is core structure for achieving IP67 and IP68 protection. If depth and width tolerances of sealing groove cavity exceed 0.005mm, compression of sealing ring at room temperature barely meets standard. However, at -40℃, plastic shell shrinks even more, significantly reducing compression of sealing ring and causing gaps. When heated to 85℃, plastic shell expands, causing localized compression of sealing ring and resulting in permanent loosening. After 500 high and low temperature cycles, leakage rate in airtightness test increases significantly. In many mold processing, sealing groove is machined in sections, dimensions of each section are not uniformly controlled, with single-section deviations ranging from 0.006 to 0.01mm. This results in inconsistent widths of formed sealing rings, uneven stress under alternating hot and cold temperatures, and premature failure of local sealing points.
2. Out-of-tolerance coaxiality of pin positioning cavity, leading to pin eccentricity and leakage after hot and cold temperatures. Dozens of metal pins are arranged on connector core; coaxiality of positioning hole cavity must be stably controlled within 0.005mm. Excessive coaxiality deviation of cavity leads to misalignment of molded core hole. While insertion and removal of pins are smooth at room temperature, repeated contraction and expansion of core during thermal cycling causes a continuous increase in hole misalignment, resulting in pin eccentricity and tilting. In high-voltage connectors, insulation distance between eccentric pins decreases, posing risks of creepage and breakdown. Unstable contact area of signal connector pins leads to signal disconnection failures.
3. Cavity dimension drift in snap-fit mechanism causes low-temperature insertion/removal jamming and high-temperature loosening. Deviations in width and wall thickness of connector mating snap-fit and locking structure cavity exceed 0.005mm. At low temperatures, plastic hardens and shrinks, reducing snap-fit clearance and drastically increasing insertion/removal resistance, sometimes preventing successful mating. At high temperatures, plastic expands and softens, resulting in insufficient snap-fit engagement. During equipment vibration, connector automatically loosens, causing a power outage and shutdown. Energy storage and vehicle-mounted equipment have stringent requirements for locking reliability; a single loosening failure can trigger a safety hazard for the entire system.
4. Uneven wall thickness in the plastic housing cavity leads to cracking during thermal cycling. Difference in cavity wall thickness at different locations on connector housing exceeds 0.005mm, resulting in uneven stress distribution within molded plastic part. During alternating hot and cold cycles, expansion and contraction rates of thick-walled and thin-walled areas are inconsistent, causing repeated stress on housing. After hundreds of aging cycles, micro-cracks appear at edges and mounting base of housing, allowing moisture to seep in and corrode metal pins. Ordinary mold processing simplifies cavity wall thickness control, relying solely on visual inspection of molded part's thickness, failing to identify micron-level wall thickness differences, leading to recurring aging and cracking problems.
Four Common Misconceptions in Industry
Misconception 1: Dimensions are acceptable at room temperature; high and low temperature aging will naturally meet standards. Room temperature only reflects static dimensions and cannot simulate cumulative deformation caused by thermal expansion and contraction. Tiny deviations within 0.005mm only become apparent after a complete temperature cycle. Misconception 2: Plastic is elastic, micro-cavity deviations can be offset by material deformation. Fiberglass-reinforced plastics are highly rigid with a very small elastic deformation range. Long-term thermal cycling can cause irreversible permanent deformation, making it impossible to compensate for dimensional deviations caused by cavity through their own elasticity. Misconception 3: Simply thickening shell can resist thermal aging. Uneven wall thickness leading to internal stress is main cause of cracking. Simply thickening shell without optimizing cavity's uniformity to 0.005mm level will not solve aging and cracking problem. Misconception 4: Mold steel is heat-resistant, so cavity dimensions won't change. While coefficient of thermal expansion of steel is fixed, inconsistent wall thickness and water channel distribution throughout cavity result in different cooling rates during molding. Residual stress in plastic molding process is determined by cavity machining precision, is not directly related to heat resistance of mold steel.

 

To ensure connector can stably withstand hundreds of high and low temperature cycling tests, all functional cavities in the entire mold must be uniformly locked with a dimensional tolerance of ±0.005mm. Standardized cavity construction design is implemented across four dimensions: sealing groove, pin positioning hole, locking clip, and shell wall thickness. This balances plastic molding stress and reduces structural damage caused by thermal deformation.
1. Uniform 0.005mm Dimension Construction for the Entire Circumferential Sealing Groove. The entire sealing groove cavity adopts a one-piece continuous processing technology, avoiding disassembly of multiple inserts and reducing splicing errors. A dimensional control point is set every 2 mm along the entire sealing groove, with groove depth and width strictly controlled at a single point tolerance of ±0.005mm. During design phase, cavity shrinkage compensation is set in zones according to thermal expansion coefficient of plastic used. Areas with large low-temperature shrinkage have a slightly larger cavity reference size, while areas with high-temperature expansion have a smaller reference size, offsetting compression fluctuation of sealing ring after 500 cycles. Corner positions of cavity adopt a uniform R-shaped transition structure to eliminate stress concentration in plastic caused by right-angle cavities, avoid corner cracking and local collapse of seal due to alternating hot and cold temperatures. After machining, three-axis coordinate measuring machine scans all points along the entire sealing groove, and only points exceeding 0.005mm tolerance range are allowed to proceed to assembly process.
2. Coaxial 0.005mm Integrated Cavity Structure for Pin Positioning Holes. All pin positioning holes are machined as a single clamping integral cavity, eliminating reference offset caused by multiple clamping operations for different hole positions. Tolerance of single hole inner diameter and hole center distance is locked at ±0.005mm, and coaxiality of all cavities for multi-row pin cores is uniformly controlled. Inner wall of positioning hole cavity has a nano-uniform polishing structure, with no local uneven machining marks. After molding, inner wall of plastic hole is smooth, sliding friction resistance of pin is stable during hot and cold cycles, preventing pin jamming and eccentricity problems. For multi-cavity connector molds, machining datum of pin positioning holes in each cavity is completely identical, eliminating deviations in hole positions between different cavities and ensuring a consistently low pin eccentricity defect rate after thermal aging of batch connectors.
3. Locking Clip Mating Cavity Clearance Quantitative Construction. Male and female locking clip cavities are designed with a pre-reserved thermal expansion compensation clearance at room temperature, with clearance value precisely calculated to within 0.005mm range. Under low-temperature contraction, minimum engagement allowance meets locking tensile force standard, and there will be no jamming or inability to pull out after high-temperature expansion at 85℃. Thickness deviation of clip's stress-bearing wall thickness throughout cavity is controlled within 0.005mm, ensuring uniform stress throughout clip after molding and preventing unilateral thinning and loosening under long-term thermal alternation. Cavity mating surface is constructed with a flat and precise structure, without machining steps, preventing localized wear and collapse of clip contact surface after aging, and ensuring long-term stable locking force.
4. Balanced Cavity Wall Thickness Control (0.005mm). Thickness difference between all corresponding wall thickness areas of connector shell and base cavity does not exceed 0.005mm. A smooth, gradual transition between thick and thin walls is designed to avoid abrupt changes in wall thickness that could cause molding stress. Conformal cooling water channels fit snugly against cavity outer wall, with a 0.005mm tolerance between water channels and cavity surface. Cooling rate is consistent across all cavities, ensuring synchronized shrinkage during plastic molding and significantly reducing probability of shell cracking under thermal cycling. During mold design phase, thermal cycling stress distribution is simulated through mold flow simulation, wall thickness and cavity dimensions are adjusted synchronously to eliminate stress concentration points in advance, mitigating aging cracks from a structural perspective.

A reasonable cavity structure design is only foundation; a complete and standardized processing flow is essential for consistently achieving micron-level tolerances. Each process incorporates control measures to eliminate cavity dimensional deviations, preventing accumulation of processing errors and amplifying risk of thermal aging failure.
1. Unified Datum Single-Setup Cavity Roughing and Finishing. Core cavities such as sealing grooves, pin positioning holes, and snap-fits utilize EROWA's unified datum tooling. Roughing, semi-finishing, and finishing are completed in a single setup without disassembling workpiece to change datum. Multiple setups can cause datum offsets exceeding 0.01mm, directly compromising 0.005mm cavity structural accuracy. Roughing is followed by a forced stress-relief annealing process to release internal stresses in steel generated during cutting, preventing slow deformation of cavity after finishing and ensuring long-term dimensional stability.
2. Micron-Level Slow Wire EDM/EDM Cavity Fine Forming. Small pin holes and narrow sealing groove cavities are machined using high-precision slow wire EDM, achieving a stable dimensional accuracy within 0.002mm. Large-area shells and snap-fit cavities utilize mirror-finish EDM layered discharge machining, with precise control of layer allowances, ensuring a cavity contour deviation of no more than 0.004mm after discharge. After EDM and wire machining, graded nano-polishing ensures a uniform surface roughness of cavity, eliminating localized unevenness and stress concentration in molded plastic, thus preventing accelerated breakage due to thermal cycling.
3. Full-Point Three-Coordinate Cavity Dimension Verification. After each mold cavity is machined, no sampling inspection is performed; instead, a full-point three-dimensional scanning inspection is conducted. Values are recorded at all controlled points, including sealing grooves, positioning holes, clips, and wall thickness. Any point exceeding ±0.005mm tolerance range requires rework and adjustment before assembly. A 0.0015mm precision three-coordinate measuring machine is used for inspection, with an error far below cavity control standard. Data is accurate and traceable, eliminating possibility of overlooking minor deviations through rough visual inspection or calipers.
4. Mold Assembly Cavity Anti-Offset Grinding Process. Splicing positions of various cavity inserts are precisely hand-ground, controlling step height difference within 0.005mm. After assembly, the overall cavity contour is continuous and without breaks. Conical surface is precisely positioned diagonally, ensuring a mold closing repeatability error of ≤0.003mm. This prevents cavity displacement after mass injection molding, guaranteeing uniform cavity dimensions and consistent thermal aging performance for each connector.
5. Thermal Cyclic Simulation Mold Verification. After mold assembly, in addition to judging passability using room temperature samples, 50 finished connectors are mass-produced and sent to a high and low temperature test chamber for 500 cycles of aging testing from -40℃ to 85℃. After aging, dimensions of sealing groove, pin hole, and snap fastener are re-measured. Dimensional changes before and after aging are compared. If deformation difference caused by cavity structure exceeds 0.005mm, mold is returned to mold end for adjustment of cavity compensation amount, a second trial molding and retest are conducted until aging dimensional fluctuations meet standards before mass production.

 

If any three of following items are present, mold's 0.005mm cavity construction cannot meet standard, connector is highly likely to fail in batches due to high and low temperature aging:
Sealing groove is split into multiple inserts and processed in sections without full-point dimensional scanning; Pin positioning holes are processed in stages without a unified processing benchmark; Only 3 to 5 points are sampled for inspection after cavity processing, resulting in incomplete scanning; Skipping stress annealing process during rough machining and directly finishing cavity; No 500-cycle high and low temperature simulated aging test molding verification is performed before mold delivery; Expansion gap of snap-fit cavity is estimated based on operator's experience, without quantitative calculation of 0.005mm; Housing cavity wall thickness difference is greater than 0.01mm, no gradual transition structure; No multi-stage precision positioning with conical surfaces, relying solely on guide pillars to control cavity position

Q1: Connector passes room temperature test, but leaks air after high and low temperature cycling. What is problem?
A: Core issue is that sealing groove cavity is machined in sections, and dimensions of each section exceed 0.005mm tolerance. Compression of sealing ring is uneven under alternating hot and cold temperatures. Replacing mold with a one-piece continuous cavity structure, controlling groove depth tolerances at all points, and incorporating a thermal expansion compensation design can solve air leakage problem.
Q2: How to improve risk of creepage in high-voltage connectors due to pin misalignment after heating and cooling?
A: Coaxiality of pin positioning holes caused by multiple clamping and machining exceeds 0.005mm. Switching to single-clamping integral cavity machining, controlling hole center distance and inner diameter tolerances with a three-axis coordinate measuring machine, significantly reduces pin misalignment defect rate after aging.
Q3: Will simply thickening shell help with appearance of micro-cracks in plastic connector housing due to aging?
A: Simply thickening shell cannot solve molding internal stress caused by excessive wall thickness differences in cavity. It is necessary to control wall thickness difference of cavity at various points in shell to within 0.005mm, setting up a smooth transition structure, and using conformal cooling water channels to eliminate potential for cracking from source of stress.
Q4: Will a 0.005mm cavity structure significantly increase mold costs?
A: While increase in mold processing costs is limited, it can save significant losses from mass aging and scrapping of connectors, repeated sample modifications, and delays in customer qualification reviews. The overall long-term mass production cost is lower, making it a cost-effective option for high-end energy storage and automotive connector projects.
Q5: If cavity deviation of a pre-formed connector mold exceeds standard, can it be repaired to achieve 0.005mm standard?
A: It depends on situation. Repairing a one-piece cavity is difficult and easily damages original reference. Modular insert structures allow for individual replacement of sealing grooves and positioning hole inserts, quickly restoring micron-level cavity size standard.
High and low temperature cycling aging is the most stringent testing item for connector products. Many manufacturers spend a lot of time adjusting plastic formulas and improving sealing ring materials, but neglect fundamental influencing factor of mold cavity structure. Seemingly small 0.005mm dimensional range directly determines upper limit of deformation of plastic parts due to thermal expansion and contraction, which is fundamental guarantee for long-term stable operation of connectors. A connector mold conforming to a precision cavity structure of 0.005mm can balance internal stress of plastic from molding source, reducing thermal deformation defects in four major structures: seal, pin, snap, and shell. This allows connector to easily withstand hundreds of cycles of extreme temperature alternation aging, ensuring stable compatibility with long-term high and low temperature operating conditions in automotive, energy storage, and photovoltaic applications.