SLS so với SLM: Quy trình gia công laser nào phù hợp với chi tiết?
SLS sinters. SLM melts. That one word difference decides which materials you can run, whether the part needs support structures, and what the surface looks like when it comes out of the chamber.
Both processes use a laser and a powder bed, which is why they get confused. They are not interchangeable and they do not compete for the same job. This page separates them by what they physically do to the powder, then by surface and tolerance, then by cost, then by the failure modes each one produces.
The one-sentence difference
SLS heats powder until the particles fuse at their contact points, which leaves the part slightly porous and needs no support because the surrounding powder holds it up. SLM melts powder completely into a liquid pool that solidifies into near-full-density metal, which needs support because nothing else holds the overhangs.
Everything downstream follows from that.
What SLS actually does
Selective Laser Sintering bonds polymer, wax or coated-sand particles without fully melting them. The laser supplies enough energy to fuse the surface of each grain to its neighbours; the grain core stays solid. The result is a part that is structurally sound at the scale of a casting mould and dimensionally stable enough for pattern work.
Two consequences matter in production. First, no support structures. The powder bed is the support, so a mould or a pattern can be nested anywhere in the build with nothing to cut off afterwards. Second, the surface is granular rather than smooth, because the part is made of partly fused grains rather than a melted pool.
In a foundry, SLS runs coated sand for moulds and cores, and PSB wax for investment casting patterns. The same machine does both — the change is powder, not hardware. That flexibility is the reason the mid-range SLS band is often the first platform a mixed shop buys.
What SLM actually does
Selective Laser Melting takes the metal powder past its melting point entirely. Each layer is a set of overlapping melt tracks that fuse into the layer below, and the finished part is 99 percent dense or better — close enough to wrought for most structural applications after heat treatment.
The support requirement is the operational cost. An overhang needs an anchor, or the melt pool sags. Those anchors are printed in the same metal, cut off by hand or by EDM afterwards, and the cut surfaces usually need finishing. On a part with a lot of overhang, support removal can take longer than the build.
SLM also builds residual stress into the part as a matter of course. The melt pool cools and contracts against the layer below, and the stress accumulates until the part is stress-relieved. Skip that step and the part will move when the supports are cut.
Side by side
| SLS | SLM | |
|---|---|---|
| What the laser does | Fuses particle surfaces | Melts the powder completely |
| Vật liệu | Coated sand, PSB wax, polymers | Stainless steel, tool steel, titanium, aluminium, superalloys |
| Mật độ | Porous at grain scale | 99%+ after processing |
| Support structures | None — the powder bed supports the part | Required on every overhang |
| Xử lý sau | Depowder, cure, inspect | Stress relief, support removal, machining, HIP where specified |
| Tốc độ xây dựng | Higher per layer, no support overhead | Lower — support and stress relief dominate calendar time |
| Best fit | Casting moulds, cores, wax patterns | Finished metal parts, thin walls, lattices |
Where each one fails
Every process has a characteristic failure. Knowing what yours looks like saves a week of arguing with a supplier.
SLS failure modes
Dimensional drift at the build edges. The powder bed near the chamber wall sits at a different temperature from the centre, and parts built at the edge come out slightly larger or slightly warped. Nest the critical dimensions toward the middle of the bed.
Nesting that ignores thermal mass. Packing a bed tightly raises the local temperature and can fuse neighbouring parts together at their closest points. A high-density bed needs a different laser energy profile than a sparse one.
Surface finish taken as a tolerance. The granular surface is not uniform, so a tolerance quoted on a nominal dimension can fail on the surface texture alone. Specify the tolerance and the surface separately.
SLM failure modes
Support removal damage. The most common cause of a scrapped SLM part is not a bad build — it is a chisel in the wrong place. Thin walls and fine lattices are the usual casualties.
Residual stress distortion. A part built without adequate stress relief will bow when the supports are cut. The distortion appears after the build, which is why it gets missed in inspection.
Porosity at the build interface. Where a part sits directly on the build plate, the first few layers see different thermal conditions and are the usual location for lack-of-fusion porosity. Machining allowance on the base solves it.
Surface finish and tolerance in practice
Suppliers quote Ra figures as though they were specifications. They are averages, and the number that matters depends on which face the tolerance sits on.
What “as-built” really means
An SLS mould comes out at roughly Ra 6 to 15 µm. That is consistent across the part because the surface is defined by grain size, not by orientation. A casting mould at that roughness needs no downstream work — the sand surface is reproduced in the casting, which is often an advantage for as-cast texture.
An SLM part comes out rougher on angled faces, because the stair-step of layer thickness shows up wherever the surface is not vertical. Horizontal top faces are the smoothest; a 45-degree face is the worst. The same part can read Ra 8 µm on one face and Ra 20 µm on another, which is why a single Ra number on a metal drawing is not a specification — it is a wish.
Where machining enters
This is where the two processes diverge in cost, not in capability. An SLS mould is used as printed. An SLM part is usually machined on every surface that carries a tolerance or a sealing face, which means fixtures, datums, a machine tool and a second operation.
The practical rule: if the drawing has a tolerance tighter than ±0.2 mm on a metal part, budget for machining before you compare processes. If the drawing is a mould or pattern with a casting tolerance of ±0.5 mm, SLS as-built will hold it.
Cost per part: the comparison that does not get published
Machine price comparisons are easy to find and mostly useless. What decides a project is cost per acceptable part, and that number includes four things the brochure leaves out.
- Machine time per part. SLS wins because there is no support overhead and the powder bed can be fully packed. SLM loses build height to supports and loses calendar time to stress relief.
- Material cost. Metal powder is the expensive consumable, and the unusable fraction depends on the alloy and the reuse policy. Coated sand and PSB wax are cheaper per kilogram by an order of magnitude.
- Post-processing labour. SLS parts go straight to depowdering and inspection. SLM parts need stress relief, support removal, and usually machining.
- Scrap rate. This is the line nobody quotes. An SLS build with a bad nesting parameter wastes powder; an SLM build with a bad support strategy wastes metal and a full machine day.
The pattern is consistent: SLS is cheaper per part at the mould-and-pattern scale, SLM is the only option when the part has to be metal. They are not competing on price. They are competing on whether the part can be a casting or has to be a finished component.
Của chúng tôi Bảng phân tích chi phí SLS works through the consumable arithmetic per build, and the metal system cost guide does the same for SLM including the post-processing line.
The question that actually decides it
Almost every SLS-versus-SLM conversation starts with the process and ends with the material. It should run the other way.
If the part is a mould, a core, or a pattern — something that exists to make a casting — the answer is SLS, because the material is sand or wax by definition. There is no SLM option.
If the part is the casting itself, or a metal component that never sees a mould, the answer is SLM. The exception is a part large enough to exceed the metal chamber but small enough to be cast, in which case printing a sand mould and casting it is both cheaper and faster than printing the metal directly.
That last case is worth stating plainly, because it is where most first projects go wrong. A 400 mm aluminium housing does not need a 400 mm SLM machine. It needs a sand mould in four days and a casting slot.
Which platform does what
Two ranges, ten platforms, no overlap. What follows is what we actually build, not a hypothetical list.
| Range | Mẫu | Thể tích khuôn (mm) | Quy trình |
|---|---|---|---|
| SLS | AFS-500 | 500 × 500 × 500 | Coated sand and PSB wax |
| LaserCore-5300 | 700 × 700 × 500 | Coated sand and PSB wax | |
| LaserCore-6000 | 1,050 × 1,050 × 650 | Coated sand and PSB wax | |
| SLM | AFS-M120 | 120 × 120 × 150 | Metal, single laser |
| AFS-M120X | 120 × 120 × 150 | Metal, two-material gradient | |
| AFS-M120XT | 120 × 150 × 150 | Metal, multi-axis gradient | |
| AFS-M300XAS | 300 × 300 × 250 | Metal, multi-material plus in-process machining |
The ranges share a control system and nothing else. The SLS 3D printer range và metal 3D printer range carry the full specifications, including the binder-jetting metal platforms that sit alongside the SLM systems.
A selection table you can use in a meeting
Five rows, decided by the part rather than the process. This is the version worth bringing to a specification review.
| The part is… | Quy trình | Because |
|---|---|---|
| A sand mould or core | SLS, coated sand | No support, no tooling, holds casting tolerance as-built |
| An investment casting pattern | SLS, PSB wax | Same platform, powder change, burnout profile already validated |
| Metal, under 300 mm, tolerant of supports | SLM | Near-full density in one operation, machined where it matters |
| Metal, under 120 mm, tight tolerance as-built | SLM single laser | Smallest chamber, best thermal uniformity, least distortion |
| Metal, over 300 mm in two axes | Print the mould, cast the part | SLM cannot clear the chamber; SLS plus a foundry slot can |
Các câu hỏi thường gặp
SLS có giống SLM không?
Không. Công nghệ SLS làm kết dính các hạt bột ở bề mặt của chúng và được sử dụng cho cát, sáp và các loại polymer. Công nghệ SLM làm nóng chảy hoàn toàn bột và được sử dụng cho kim loại. Sự khác biệt này quyết định loại vật liệu, yêu cầu về khung đỡ và mật độ của chi tiết thành phẩm.
SLS có thể in kim loại không?
Không. Công nghệ SLS không thể đạt được nhiệt độ hoặc tính chất nóng chảy cần thiết để nén chặt bột kim loại. Đối với kim loại, các quy trình được sử dụng là SLM hoặc in phun chất kết dính.
Tại sao công nghệ SLM cần giá đỡ còn công nghệ SLS thì không?
Bởi vì các chi tiết SLS được đặt trong lớp bột chưa nung kết, giúp giữ chúng cố định. Trong công nghệ SLM, lớp bột xung quanh vùng nóng chảy không có tính kết cấu, do đó phần nhô ra cần có điểm neo được in sẵn, nếu không nó sẽ sụp đổ. Việc loại bỏ các cấu trúc hỗ trợ là một phần chi phí cố định trong quy trình SLM.
Cái nào nhanh hơn?
Với công nghệ SLS, mỗi chi tiết đạt tiêu chuẩn đều có thể được sản xuất. Không cần loại bỏ các cấu trúc hỗ trợ và bề mặt in có thể được lấp đầy đến tận mép. Công nghệ SLM mất thời gian cho quá trình giảm ứng suất và chiều cao in bị hạn chế do các cấu trúc hỗ trợ, do đó việc so sánh năng suất chỉ dựa trên tốc độ laser là không chính xác.
Loại bề mặt nào tốt hơn?
Cả hai phương pháp này đều không cho bề mặt hoàn thiện tốt ngay từ khi hoàn thành. Công nghệ SLS tạo ra bề mặt có độ nhám đồng đều, khoảng từ Ra 6 đến 15 micromet. Công nghệ SLM cho bề mặt thô hơn ngay từ khi hoàn thành, với hiện tượng bậc thang trên các mặt nghiêng, nhưng có thể gia công để đạt độ hoàn thiện tốt hơn nhiều do vật liệu là kim loại. Câu hỏi đặt ra là liệu chi tiết đó có thực sự cần phải gia công hay không.
Bài đọc liên quan
For the material side of the same decision, 3D printing steel covers the grades that actually run. For the machine side, máy in 3D kim loại công nghiệp lists the seven platforms with build volumes.
The wax side of the SLS range, including what a pattern costs against an injection die, is in wax 3D printer price.Tell us what the part is
Send the geometry, the material and the annual volume. We will tell you which laser process fits — and in the cases where neither does, we will say that instead. A part that should be machined from solid or cast from a printed mould is not improved by printing it in metal.
