{"id":8124,"date":"2026-10-07T10:00:00","date_gmt":"2026-10-07T02:00:00","guid":{"rendered":"https:\/\/maxtormetal.com\/?p=8124"},"modified":"2026-10-07T22:31:22","modified_gmt":"2026-10-07T14:31:22","slug":"grid-blade-snapping-slot-fillet-radius-r02mm-fix","status":"publish","type":"post","link":"https:\/\/maxtormetal.com\/vi\/grid-blade-snapping-slot-fillet-radius-r02mm-fix\/","title":{"rendered":"Kh\u1eafc ph\u1ee5c g\u00e3y dao l\u01b0\u1edbi t\u1ea1i \u0111\u00e1y r\u00e3nh: B\u00e1n k\u00ednh bo R, \u0111\u1ed9 nguy\u00ean v\u1eb9n EDM v\u00e0 ki\u1ec3m so\u00e1t ram hai l\u1ea7n cho thi\u1ebft k\u1ebf R\u22650,2 mm"},"content":{"rendered":"
\"Schematic<\/figure><\/div>

T\u00f3m t\u1eaft nhanh:<\/strong> Hi\u1ec7n t\u01b0\u1ee3ng g\u00e3y dao d\u1ea1ng l\u01b0\u1edbi t\u1ea1i \u0111\u00e1y r\u00e3nh do s\u1ef1 k\u1ebft h\u1ee3p c\u1ee7a ba y\u1ebfu t\u1ed1: s\u1ef1 t\u1eadp trung \u1ee9ng su\u1ea5t \u0111\u00e0n h\u1ed3i cao (Kt 7\u201312 \u0111\u1ed1i v\u1edbi c\u00e1c r\u00e3nh g\u00f3c nh\u1ecdn), c\u00e1c khuy\u1ebft t\u1eadt b\u1ec1 m\u1eb7t \u0111\u00f3ng vai tr\u00f2 l\u00e0 \u0111i\u1ec3m kh\u1edfi ph\u00e1t v\u1ebft n\u1ee9t (l\u1edbp \u0111\u00fac l\u1ea1i do EDM, v\u1ebft ch\u00e1y m\u00e0i) v\u00e0 \u0111\u1ed9 d\u1ebbo dai kh\u00f4ng \u0111\u1ee7 c\u1ee7a v\u1eadt li\u1ec7u. Gi\u1ea3i ph\u00e1p k\u1ef9 thu\u1eadt c\u1ed1t l\u00f5i l\u00e0 quy \u0111\u1ecbnh b\u00e1n k\u00ednh bo \u0111\u00e1y r\u00e3nh R\u22650,2 mm \u2014 gi\u00fap gi\u1ea3m h\u1ec7 s\u1ed1 Kt kho\u1ea3ng m\u1ed9t n\u1eeda so v\u1edbi h\u00ecnh h\u1ecdc R0,05 mm \u2014 k\u1ebft h\u1ee3p v\u1edbi vi\u1ec7c lo\u1ea1i b\u1ecf ho\u00e0n to\u00e0n l\u1edbp \u0111\u00fac l\u1ea1i EDM b\u1eb1ng c\u00e1c l\u00e1t c\u1eaft tinh (skim cuts) v\u00e0 \u0111\u00e1nh b\u00f3ng, c\u00f9ng quy tr\u00ecnh nhi\u1ec7t luy\u1ec7n ram hai l\u1ea7n (double-temper) ph\u00f9 h\u1ee3p v\u1edbi m\u00e1c th\u00e9p c\u1ee5 th\u1ec3. Trong m\u1ed9t tr\u01b0\u1eddng h\u1ee3p th\u1ef1c t\u1ebf \u0111\u01b0\u1ee3c ghi nh\u1eadn v\u1edbi dao l\u01b0\u1edbi m\u00e1y th\u00e1i h\u1ea1t l\u1ef1u \u1edf \u0111\u1ed9 c\u1ee9ng HRC 56\u201358, vi\u1ec7c ki\u1ec3m so\u00e1t b\u00e1n k\u00ednh \u0111\u00e1y r\u00e3nh \u1edf m\u1ee9c R0,20 mm \u0111\u00e3 gi\u1ea3m kho\u1ea3ng 55\u201365% s\u1ed1 l\u1ea7n thay dao kh\u1ea9n c\u1ea5p v\u00e0 gi\u1ea3m kho\u1ea3ng 45\u201355% th\u1eddi gian d\u1eebng m\u00e1y kh\u00f4ng k\u1ebf ho\u1ea1ch.<\/p><\/blockquote>

Hi\u1ec7n t\u01b0\u1ee3ng g\u00e3y dao d\u1ea1ng l\u01b0\u1edbi l\u00e0 m\u1ed9t trong nh\u1eefng d\u1ea1ng h\u01b0 h\u1ecfng g\u00e2y gi\u00e1n \u0111o\u1ea1n nghi\u00eam tr\u1ecdng v\u00e0 d\u1ec5 b\u1ecb hi\u1ec3u sai nh\u1ea5t trong c\u00e1c v\u1eadn h\u00e0nh x\u1ea3 b\u0103ng (slitting) v\u00e0 c\u1eaft l\u01b0\u1edbi t\u1ed1c \u0111\u1ed9 cao. Khi dao b\u1ecb g\u00e3y t\u1ea1i v\u1ecb tr\u00ed \u0111\u00e1y r\u00e3nh, h\u1eadu qu\u1ea3 x\u1ea3y ra ngay l\u1eadp t\u1ee9c: th\u1eddi gian d\u1eebng m\u00e1y kh\u00f4ng k\u1ebf ho\u1ea1ch, s\u1ee5t gi\u1ea3m t\u1ef7 l\u1ec7 s\u1ea3n ph\u1ea9m \u0111\u1ea1t ngay t\u1eeb l\u1ea7n \u0111\u1ea7u (FPY) v\u00e0 k\u00e9o theo m\u1ed9t lo\u1ea1t s\u1ef1 c\u1ed1 ch\u1ea5t l\u01b0\u1ee3ng th\u1ee9 c\u1ea5p tr\u00ean cu\u1ed9n d\u1ea3i. \u0110\u1ed1i v\u1edbi c\u00e1c qu\u1ea3n l\u00fd s\u1ea3n xu\u1ea5t v\u00e0 tr\u01b0\u1edfng b\u1ed9 ph\u1eadn thi\u1ebft b\u1ecb v\u1eadn h\u00e0nh c\u00e1c d\u00e2y chuy\u1ec1n gia c\u00f4ng cu\u1ed9n li\u00ean t\u1ee5c, ch\u1ec9 m\u1ed9t s\u1ef1 c\u1ed1 g\u00e3y dao c\u00f3 th\u1ec3 ng\u1ed1n h\u00e0ng gi\u1edd b\u1ea3o tr\u00ec s\u1eeda ch\u1eefa v\u00e0 t\u1ea1o ra l\u01b0\u1ee3ng ph\u1ebf li\u1ec7u l\u00e0m b\u00e0o m\u00f2n l\u1ee3i nhu\u1eadn h\u00e0ng th\u00e1ng.<\/p>

Nguy\u00ean nh\u00e2n g\u1ed1c r\u1ec5 h\u1ea7u nh\u01b0 lu\u00f4n l\u00e0 do s\u1ef1 t\u1eadp trung \u1ee9ng su\u1ea5t sinh ra t\u1eeb thi\u1ebft k\u1ebf \u2014ho\u1eb7c m\u1ed9t khuy\u1ebft t\u1eadt trong qu\u00e1 tr\u00ecnh gia c\u00f4ng ch\u01b0a t\u1eebng \u0111\u01b0\u1ee3c ph\u00e1t hi\u1ec7n. \u0110\u1ed1i v\u1edbi dao c\u00f3 r\u00e3nh, \u0111\u00e1y r\u00e3nh l\u00e0 \u0111i\u1ec3m ch\u1ecbu \u1ee9ng su\u1ea5t cao nh\u1ea5t tr\u00ean to\u00e0n b\u1ed9 th\u00e2n dao. N\u1ebfu kh\u00f4ng c\u00f3 s\u1ef1 ki\u1ec3m so\u00e1t h\u00ecnh h\u1ecdc h\u1ee3p l\u00fd v\u00e0 \u0111\u1ed9 d\u1ebbo dai kim lo\u1ea1i ph\u00f9 h\u1ee3p, s\u1ef1 kh\u1edfi ph\u00e1t v\u1ebft n\u1ee9t ch\u1ec9 l\u00e0 v\u1ea5n \u0111\u1ec1 th\u1eddi gian.<\/p>

Gi\u1ea3i ph\u00e1p n\u1eb1m \u1edf chi\u1ebfn l\u01b0\u1ee3c k\u1ef9 thu\u1eadt k\u00e9p. Th\u1ee9 nh\u1ea5t, quy \u0111\u1ecbnh v\u00e0 ki\u1ec3m tra b\u00e1n k\u00ednh bo \u0111\u00e1y r\u00e3nh R\u22650,2 mm \u0111\u1ec3 gi\u1ea3m r\u00f5 r\u1ec7t h\u1ec7 s\u1ed1 t\u1eadp trung \u1ee9ng su\u1ea5t \u0111\u00e0n h\u1ed3i (Kt) t\u1ea1i ch\u00e2n r\u00e3nh. Th\u1ee9 hai, \u00e1p d\u1ee5ng quy tr\u00ecnh nhi\u1ec7t luy\u1ec7n ram hai l\u1ea7n (double-temper) \u0111\u01b0\u1ee3c \u0111i\u1ec1u ch\u1ec9nh ch\u00ednh x\u00e1c nh\u1eb1m t\u1ed1i \u0111a h\u00f3a \u0111\u1ed9 d\u1ebbo dai c\u1ee7a v\u1eadt li\u1ec7u xung quanh g\u00f3c bo \u0111\u00f3. H\u1ed7 tr\u1ee3 cho c\u1ea3 hai chi\u1ebfn l\u01b0\u1ee3c l\u00e0 ba k\u1ef7 lu\u1eadt c\u00f4ng ngh\u1ec7 th\u01b0\u1eddng b\u1ecb b\u1ecf qua khi mua s\u1eafm d\u1ee5ng c\u1ee5 c\u1eaft: lo\u1ea1i b\u1ecf ho\u00e0n to\u00e0n l\u1edbp \u0111\u00fac l\u1ea1i do EDM, ng\u0103n ng\u1eeba nghi\u00eam ng\u1eb7t v\u1ebft ch\u00e1y m\u00e0i v\u00e0 kh\u1eed \u1ee9ng su\u1ea5t d\u01b0 tr\u01b0\u1edbc khi ki\u1ec3m tra nghi\u1ec7m thu cu\u1ed1i c\u00f9ng.<\/p>

Ghi ch\u00fa k\u1ef9 thu\u1eadt:<\/strong> If your specification for slotted grid blades requires documented fillet radius verification, EDM process records, and heat-treat batch traceability, see Maxtor Metal’s reference page on th\u00e9p b\u0103ng l\u00e0m l\u01b0\u1ee1i dao c\u00f4ng nghi\u1ec7p d\u1ea1ng cu\u1ed9n v\u00e1t c\u1ea1nh<\/em><\/strong><\/a> for supply specifications and documentation standards applicable to precision slotted blade geometries.<\/p>

B\u00e0i vi\u1ebft n\u00e0y s\u1ebd \u0111i qua t\u1eebng y\u1ebfu t\u1ed1 c\u1ee7a chi\u1ebfn l\u01b0\u1ee3c k\u00e9p theo tr\u00ecnh t\u1ef1: c\u01a1 h\u1ecdc g\u00e2y ra n\u1ee9t g\u00e3y t\u1ea1i \u0111\u00e1y r\u00e3nh, c\u00e1ch h\u00ecnh h\u1ecdc g\u00f3c bo gi\u1ea3m thi\u1ec3u h\u1ec7 s\u1ed1 Kt m\u1ed9t c\u00e1ch \u0111\u1ecbnh l\u01b0\u1ee3ng, c\u00e1c ki\u1ec3m so\u00e1t to\u00e0n v\u1eb9n khi gia c\u00f4ng EDM v\u00e0 m\u00e0i, c\u00e1ch l\u1ef1a ch\u1ecdn th\u00f4ng s\u1ed1 ram theo m\u00e1c th\u00e9p, v\u00e0 c\u00e1c \u0111i\u1ec3m ki\u1ec3m tra nghi\u1ec7m thu ho\u00e0n t\u1ea5t quy tr\u00ecnh tr\u01b0\u1edbc khi dao \u0111\u01b0a v\u00e0o v\u1eadn h\u00e0nh.<\/p>

T\u1ea1i sao \u0111\u00e1y r\u00e3nh lu\u00f4n l\u00e0 v\u1ecb tr\u00ed \u0111\u1ea7u ti\u00ean b\u1ecb g\u00e3y tr\u00ean dao d\u1ea1ng l\u01b0\u1edbi<\/h2>
\"T\u1ea1i<\/figure><\/div>

Stress Concentration at Slot Bottoms<\/h3>

In a slotted blade under bending or cyclic cutting loads, stress is not distributed uniformly across the cross-section. It concentrates sharply at geometric discontinuities \u2014 and no feature on a slotted blade creates a sharper discontinuity than a tight slot root.<\/p>

The theoretical stress concentration factor Kt relates the peak local stress \u03c3 max to the nominal applied stress \u03c3 nom:<\/p>

Kt = \u03c3 max \/ \u03c3 nom<\/strong><\/p><\/blockquote>

For a rectangular slot in a finite plate, Kt is strongly influenced by the ratio of the root radius r<\/em> to the slot half-width b<\/em> (or depth t<\/em>, depending on the reference model). When r<\/em> approaches zero \u2014 as it does with a square-cornered slot \u2014 Kt climbs toward singularity. Even at r<\/em> = 0.05 mm, Kt values of 8\u201312 are common in tight-slot geometries at industrial blade scales. At those multipliers, a nominal bending stress of 300 MPa becomes a local stress exceeding 2,400 MPa \u2014 well above the fracture toughness threshold for most high-carbon tool steels in the hardened-and-lightly-tempered condition.<\/p>

The slot bottom is therefore not just a stress concentration \u2014 it is the single most failure-critical feature in the tool design. Every process decision downstream of design \u2014 EDM strategy, grinding pass depth, tempering protocol, final inspection \u2014 must be evaluated in the context of what it does to that slot root.<\/p>

Crack Initiation Sources in Slots<\/h3>

Even with adequate fillet geometry, cracks can initiate at slot bottoms when surface or subsurface defects provide nucleation sites. The three most consequential defect sources in slotted blade manufacture are:<\/p>

1. EDM recast (white) layer.<\/strong> Wire-EDM and sinker-EDM are standard processes for producing slots in hardened or semi-hardened tool steel. Both leave a resolidified, amorphous surface layer typically 2\u201325 \u00b5m thick. This layer is harder and more brittle than the base matrix \u2014 Vickers hardness values above 1,100 HV are common \u2014 and it contains tensile residual stresses and microcracks from the rapid resolidification thermal cycle. These microcracks are structural initiators under cyclic load. If left in place, they can propagate into the substrate within the first few thousand blade strokes.<\/p>

2. Grinding-induced microcracks.<\/strong> Aggressive grinding after EDM \u2014 particularly with insufficient coolant delivery or excessive wheel speed \u2014 generates localized heat that causes surface temper, re-hardening, or micro-cracking. In the slot root geometry, where wheel access is restricted, coolant starvation is a persistent process risk.<\/p>

3. Quench-induced residual tensile stress.<\/strong> During hardening, differential thermal contraction between the blade surface and core \u2014 particularly in the thin-wall regions around slots \u2014 generates residual tensile stresses. Without adequate stress-relief tempering, these stresses add directly to applied service stresses, reducing the effective fracture margin.<\/p>

Role of Residual Tensile Stress<\/h3>

Residual stress is invisible to the inspector who uses only a hardness tester and a visual check. But it is fully additive to applied stress in the fracture-mechanics sense. A slot bottom carrying 150 MPa of residual tensile stress from quench shrinkage, combined with a 300 MPa applied bending stress and a Kt of 6, experiences a local stress state of approximately:<\/p>

\u03c3 local \u2248 Kt \u00d7 (\u03c3 applied + \u03c3 residual) = 6 \u00d7 450 MPa = 2,700 MPa<\/p><\/blockquote>

Most high-alloy tool steels in service condition have plane-strain fracture toughness (KIC) between 20 and 35 MPa\u00b7m\u2070\u00b7\u2075 \u2014 but the range is wide because it spans different grades and heat-treat states.<\/p>

For reference: D2 (1.2379) at HRC 58\u201362 typically shows KIC of 18\u201322 MPa\u00b7m\u2070\u00b7\u2075; M2 (1.3343) at HRC 62\u201365 is typically 20\u201325 MPa\u00b7m\u2070\u00b7\u2075; H13 (1.2344) at HRC 44\u201350 (lower hardness, higher toughness application) can reach 28\u201338 MPa\u00b7m\u2070\u00b7\u2075. When selecting a blade grade for a slotted geometry application, the KIC value at the intended service hardness \u2014 not an average range \u2014 is the relevant design input.<\/p>

Thi\u1ebft k\u1ebf b\u00e1n k\u00ednh bo \u0111\u00e1y r\u00e3nh (Fillet Radius Design)<\/h2>
\"Thi\u1ebft<\/figure><\/div>

Why R\u22650.2 mm Reduces Kt<\/h3>

The relationship between fillet radius and Kt is nonlinear: the benefit is largest in the lower radius range, meaning the transition from R0.05 mm to R0.2 mm delivers a larger Kt reduction than the transition from R0.5 mm to R1.0 mm.<\/p>

Using normalized stress concentration charts from Pilkey & Pilkey, Peterson’s Stress Concentration Factors<\/em> (3rd ed., Wiley, 2008) for a slot in a finite-width plate under in-plane loading:<\/p>

Slot Root Radius r (mm)<\/th>Approximate Kt (typical slot geometry)<\/th><\/tr>
0.05<\/td>10\u201312<\/td><\/tr>
0.10<\/td>7\u20138<\/td><\/tr>
0.20<\/td>4.5\u20135.5<\/td><\/tr>
0.30<\/td>3.5\u20134.0<\/td><\/tr>
0.50<\/td>2.5\u20133.0<\/td><\/tr><\/tbody><\/table><\/figure>

The move from R0.05 mm to R0.20 mm cuts Kt roughly in half. If the material’s fracture resistance is held constant, halving Kt more than doubles the load-carrying capacity before crack initiation. Alternatively, at equivalent loads, halving Kt can extend fatigue life by an order of magnitude or more, depending on the fatigue crack growth exponent for the specific steel grade.<\/p>

R0.2 mm is therefore a practical engineering minimum<\/strong>, not an arbitrary specification. It is the radius below which Kt rises sharply enough that even modest process variation \u2014 residual stress, surface defects, minor EDM recast remnants \u2014 pushes the slot bottom into reliable fracture territory.<\/p>

Selecting Radius and Tolerances<\/h3>

Selecting the target radius requires balancing three competing constraints:<\/p>

  1. Stress concentration reduction<\/strong> \u2014 a larger r<\/em> is always mechanically beneficial.<\/li>\n\n
  2. Slot dimensional function<\/strong> \u2014 the slot must still guide the strip or lock the grid pattern correctly. A root that is too large can interfere with a mating feature or alter the spring rate of thin blade webs.<\/li>\n\n
  3. Manufacturability<\/strong> \u2014 the radius must be achievable and measurable by the processes in use (EDM skim cut, grinding, polishing).<\/li><\/ol>

    For most industrial grid blade geometries, a target of R0.20 \u00b1 0.05 mm<\/strong> is achievable with wire-EDM skim cuts followed by stone polishing, and is tight enough to maintain slot function while achieving the required Kt reduction. In thicker blades with deeper slots, R0.30\u20130.50 mm may be practical and should be evaluated where slot function permits.<\/p>

    Specify the tolerance unilaterally on engineering drawings: the minimum radius is the structural requirement; the maximum is a fit\/function constraint. A notation of R0.20 min \/ R0.30 max makes this explicit and avoids the common shop-floor ambiguity of “rounding out the corner” without a defined upper limit.<\/p>

    Measuring and Verifying Radii<\/h3>

    Slot root radii in the R0.2\u2013R0.5 mm range require instrument-grade measurement. Acceptable methods include:<\/p>